Trent John Alexander-Arnold^[13] was born on 7 October 1998^[14] in the West Derby suburb of Liverpool, Merseyside.^[15] He attended St Matthew's Catholic Primary School, before later enrolling at St Mary's College in Crosby.^[16][17][18]When he was six years old, local football club Liverpool hosted a half-term camp to which a number of pupils from his school were invited, and his was one of the names drawn from a hat to attend. There, he was spotted by academy coach Ian Barrigan who subsequently approached his parents to offer him the chance to join the club's academy. He began training two-to-three times a week, and in a variety of different positions, before later going on to captain the club at U16 and U18 level under coach Pepijn Lijnders.^{[19][20][21][22][23]} In the intervening period, at the age of 14, he left St Mary's to enroll at Rainhill High School, an educational institution which shares an affiliation with the football club.^[24]

During his time in Liverpool's academy, Alexander-Arnold converted from a wide midfielder to a right-back.^[25] It was the position that offered him the clearest path to the first team and he excelled in his new role, being singled out by former Liverpool captain Steven Gerrard, who tipped him to have a bright future at the club in his autobiography.^[19][26] As a result of his rapid progression, and in the buildup to the 2015–16 season, Alexander-Arnold was selected in the first team squad by manager Brendan Rodgers for the team's final pre-season friendly against Swindon Town where he marked his unofficial debut for the club in a 2–1 win.^[27][28]

Having previously taken part in Liverpool's pre-season tour of the United States, Alexander-Arnold made his professional debut on 25 October 2016, starting in a 2–1 victory over Tottenham Hotspur in the fourth round of the EFL Cup. He was booked in the first half for a foul on Ben Davies, which he later revealed could have ended in him being sent off, before being substituted for first-choice right-back Nathaniel Clyne in the 68th minute.^[19][29][30] Despite the indiscretion, his performance earned a spot in the EFL Cup Team of the Round alongside teammate Daniel Sturridge.^[31][32]

Alexander-Arnold's breakthrough into the first team was rewarded with a new long-term contract in November and he started in Liverpool's next EFL Cup match later that month against Leeds United. He was named man of the match for his performance after registering his first assist for the club by setting up striker Divock Origi for the opening goal of a 2–0 win for Liverpool.^[33][34][35] He then made his Premier League debut on 14 December, coming on as a late substitute in a 3–0 win over Middlesbrough, and made his first league start in a 1–1 draw with Manchester United on 15 January 2017.^[36][37] In May, having made 12 appearances across all competitions, he was named Liverpool's Young Player of the Season and was also nominated for the Premier League 2 Player of the Season award.^{[38][39][40][41]}

In the buildup to the 2017–18 season, regular right-back Clyne suffered a serious back injury which afforded Alexander-Arnold the opportunity to rotate with Joe Gomez during the early stages of the campaign.^[42] On 15 August 2017, he scored his first goal for the club when he struck home from a free kick in a 2–1 first leg Champions League play-off round win over Bundesliga team 1899 Hoffenheim.^[43] In doing so, he became the third youngest player to score on his European debut for Liverpool, after Michael Owen and David Fairclough.^[44] During the group stages of the competition, Alexander-Arnold scored again in a 7–0 Champions League win over Maribor on 17 October, a result which was the joint-largest ever away win in the competition, and largest away win by an English club.^[45] He then scored his first Premier League goal for Liverpool on 26 December in a 5–0 home win over Swansea City.^[46]

In March the following year, Alexander-Arnold endured his most difficult spell with the club to date, after struggling against Crystal Palacewinger Wilfried Zaha and Manchester United's Marcus Rashford in successive weeks.^[19]Nonetheless, he retained his position in Liverpool's starting line-up to become the youngest English player to start in a Champions League quarter-final match and performed strongly in a 3–0 win over English rivals Manchester City in April. His performance saw him named man of the match and earned him praise from the media for his ability to nullify City winger Leroy Sané.^[47][48] He impressed again in the reverse fixture as Liverpool eliminated City 5–1 on aggregate to advance to the semi-finals of the competition for the first time in 10 years.^[49]On 10 May, his domestic and European form was rewarded when he won the Liverpool Young Player of the Season award for the second season running.^[50] Later that month, he became the youngest Liverpool player to start in a Champions League final when he was named in the starting line-up against two-time reigning champions, Real Madrid. Tasked with marking Cristiano Ronaldo, he performed admirably though Liverpool ultimately succumbed to a 3–1 defeat.^[51][52]Following the conclusion of the season, in which he scored three goals in 33 appearances across all competitions, he was nominated for the Golden Boy award where he was later voted runner-up to Ajax defender, Matthijs de Ligt.^[53][54]

During the early stages of the following season, he made his 50th appearance for Liverpool when he started in a 2–1 victory over Tottenham; the same opposition against whom he had made his debut almost two years prior.^[55] In October, he was one of 10 players nominated for the inaugural Kopa Trophy, an award presented by France Football to the best young player under the age of 21, and ultimately ended sixth in the voting polls, having received votes from Owen, Denis Law and Pavel Nedvěd.^[56][57] He continued to enhance his burgeoning reputation in the months thereafter and was consistently listed in reports by the CIESas the world's most valuable full-back from a transfer value perspective.^[58][59] Alexander-Arnold elevated his game further following the turn of the year and, on 27 February 2019, became the youngest player, aged 20 years and 143 days, to record three assists in a single Premier League match when he set up Sadio Mané twice and Virgil van Dijk once in a 5–0 win over Watford.^[60] Less than two months later, he became the fifth-youngest player to reach 50 Premier League appearances for the club, behind Owen, Raheem Sterling, Robbie Fowler and Gerrard, when he started in a 3–1 win over Southampton.^[61][62] His domestic form was rewarded later in April when he was nominated for the PFA Young Player of the Year award, although the award was won by Manchester City's Sterling, and he was later named in the PFA Team of the Year alongside Liverpool teammates Van Dijk, Mané and Andrew Robertson.^[63][64][65]

Alexander-Arnold's creative prowess came to the fore once again in May when, during a 3–2 win over Newcastle United, Alexander-Arnold equalled the Premier League record for the most assists by a defender in a season, with his two assists in the match raising his tally to 11. It also saw him and Robertson, who had 11 assists of his own, become the first set of defenders from the same team to record double figures for assists in the same season.^[66] Three days later, with Liverpool trailing Barcelona 3–0 on aggregate after a first-leg defeat, he recorded two more assists, including an "instinctive corner" for Origi's winning goal, to help the club to a 4–3 aggregate victory and progress to a second consecutive Champions League final.^[67] On the final day of the domestic season, Alexander-Arnold assisted Mané in a 2–0 win over Wolverhampton Wanderers to break the Premier League record for the most assists by a defender in a domestic campaign, with 12, surpassing previous holders Andy Hinchcliffe, Leighton Baines and Robertson.^[68][69] He then started in the Champions League Final, a 2–0 win over Tottenham, and became the youngest player to start in two successive finals in the competition, breaking the record set by A.C. Milan's Christian Panucci in 1995.^[70] He was later named in the competition's Team of the Season and nominated for the Defender of the Season award.^[71][72]

Alexander-Arnold began the 2019–20 season with his position as Liverpool's right-back cemented, and provided the assist for Origi's goal in the club's 4–1 opening game win over Norwich City.^[73] In doing so, he became only the eighth player in the Premier League era to register an assist in five consecutive games, and the first to do so for Liverpool.^[74] He appeared in subsequent wins over Southampton and Arsenal, as well as in Liverpool's triumph over Chelsea in the UEFA Super Cup where he scored a penalty in the shoot-out.^[75] He then scored his first goal of the season during Liverpool's 2–1 league win over the Blues from a set-piece routine that was later nominated for the Premier League Goal of the Month award.^[76] The following month, he was nominated for the 2019 Ballon d'Or award, alongside six of his Liverpool teammates.^[77]

On 2 November, at the age of 21 years and 26 days, he became the fourth-youngest player to reach 100 appearances for Liverpool, behind Owen, Sterling and Fowler, and marked the occasion by assisting Mané for the winning goal in a 2–1 victory over Aston Villa.^[78] Exactly one month later, he was voted as the 19th-best player in the world at the Ballon d'Or ceremony, and the highest-ranked full-back.^[79][80] He then made his FIFA Club World Cup debut during Liverpool's 2–1 semi-final win over reigning CONCACAFchampions Monterrey, and provided the match-winning assist for Roberto Firmino in stoppage time after coming on as a substitute for James Milner.^[81] Three days later, he started and played the full 120 minutes as Liverpool were crowned champions for the first time in the club's history following a 1–0 win after extra time over Copa Libertadores champions Flamengo.^[82]

Upon returning from Qatar, Liverpool recorded a 4–0 league win over second-placed Leicester Cityduring a match in which Alexander-Arnold played a hand in all four goals by scoring one, assisting two, and winning a penalty which was converted by Milner.^[83] He was later rewarded for his form with the Premier League Player of the Monthaward, becoming the first full-back to claim the honour since Micah Richards in 2007.^[84] Further recognition followed at the turn of the year, when he was named in the 2019 UEFA Team of the Year.^[85] Alexander-Arnold then played a starring role in Liverpool's 2–1 win over Wolves as the club extended their unbeaten run in the league to 40 matches. During the encounter, he assisted captain Jordan Henderson for the opening goal and in the process became the first defender in the competition's history to reach double figures for assists in multiple campaigns.^[86]

Towards the end of February, following a 3–2 win over West Ham United, he matched his league assist record from the season before and took his overall tally in the Premier League to 25, becoming the third-youngest player in the competition's history to reach a quarter-century of assists behind Cesc Fàbregas and Wayne Rooney.^[87] The season was temporarily suspended between March and June due to the outbreak of the COVID-19 pandemic, following which Alexander-Arnold helped Liverpool win their first league title in 30 years, and their first in the Premier League era.^[88] With the title secured, he then broke his own assist record on the penultimate day of the season when he set Firmino up to score in a 5–3 win over Chelsea.^[89]For his contributions during the season, he was awarded the inaugural Premier League Young Player of the Season award, won the PFA Young Player of the Year accolade and was named in the PFA Team of the Year.^[90][91][92]

Alexander-Arnold continued to feature prominently for Liverpool during the 2020–21 season and, on 9 December, became the youngest player to captain the club in European competition, and third-youngest in any competition, when he donned the armband during a 1–1 Champions League draw against Midtjylland.^[93] Later that month, he was named in the 2020 FIFA FIFPro Men's World 11 alongside teammates Alisson, Van Dijk and Thiago, althewhile Liverpool set about its domestic title defence by topping the league standings by Christmas.^[94][95]