Alex Oxlade-Chamberlain, who had been training at the Southampton Academy since he was seven, made his first-team debut for the club in a 5-0 win over Huddersfield Town on March 2, 2010. At the age of 16 years 199 days, he became the Saints second youngest player ever, after Theo Walcott, to make an appearance for the Saints
In the final match of the season against Southend United on March 8, 2010, he came as an 82nd-minute substitute for Jason Puncheon. On August 10, 2010, he made his first competitive start against Bournemouth in the first round of the League Cup, in which he scored his first senior goal in a 2-0 victory.
Following his 17th birthday, he signed his first professional contract on August 20, 2010 and made his first league start in a 2–0 loss to Rochdale on September 4, 2010. The following month, he scored the winning goal against Oldham Athletic on October 23, 2010, followed by two more goals and an assist against Dagenham & Redbridge on November 2, 2010.
With nine goals during the 2010-11 season, he helped the club make to the EFL Championship and was named in the 'PFA League One Team of the Year'. Soon after, his father stated that he should join Arsenal to continue his development, following which, he got signed to the Premier League club on August 8, 2011 for an estimated £15 million.
He became the 150th player to represent Arsenal in the Premier League following his debut on August 28, 2011 as a 62nd-minute substitute in 8–2 defeat against Manchester United. His first goal for the club came in a League Cup match against Shrewsbury Town on September 20, 2011, which he scored with a kick from 25 yards.
On his UEFA Champions League debut against Greek team Olympiacos on September 28, 2011, he scored the opening goal eight minutes into the game, and became the youngest Englishman to score in the Champions League. He contributed in an assist on his Premier League debut against Manchester United on January 22, 2012, however, the match ended in a 2-1 loss after he was substituted in the 78th minute.
He scored his first two Premier League goals in a 7–1 home win against Blackburn Rovers on February 4, 2012. He finished the season as the youngest player to be nominated for the 'PFA Young Player of the Year' award.
In 2012–13, his only League Cup goal was from 25 yards in a 6–1 victory against Coventry City and his sole Premier League goal was in a 7–3 win against Newcastle United. In December 2012, he signed a long term contract with Arsenal.
He began the 2013–14 season assisting in the only goal in a 3-1 defeat against Aston Villa, but sustained an injury that kept him out of the field for months. However, he still managed to earn nomination for the Golden Boy Award 2013, and on his return, scored both goals in Arsenal's 2–0 win over Crystal Palace on February 2nd, 2014.
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During the 2014–15 season he helped Arsenal beat Manchester City by 3–0 to win the 2014 FA Community Shield and went on to score against Tottenham, RSC Anderlecht and Monaco. He was sidelined for weeks after sustaining injury during their FA Cup win against Manchester United, and returned as a substitute in the '2015 FA Cup Final' against Aston Villa.
In the following season, he scored the only goal against Chelsea in the Community Shield match and scored another goal against Bournemouth, his first away goal in a league match for Arsenal. He suffered a serious knee injury during their Champions League match against Barcelona on February 23, 2016, which was aggravated by another injury in May during training session, keeping him out for the season.
He scored several goals and assisted in many more during the 2016–17 season, including the second goal in a 3–4 defeat against Liverpool and another against West Ham United. With three goals in the EFL Cup, he helped Arsenal reach the quarter-finals, and bagged the 'Man of the Match' award in the FA Cup semi-final against Manchester City for his assist in the equalizer.
He signed a £35 million five-year contract with Liverpool on August 31, 2017 and made his debut for the club as a substitute in a 5–0 loss to Manchester City on September 9, 2017. His first goal for Liverpool was in a 7–0 Champions League win over Maribor, followed by his first league goal in a 4–1 victory over West Ham.