Deployed as a fullback, Flanagan currently plays for Liverpool in the Premier League and the England national football team. He made his debut for Liverpool in a 3-0 win against Manchester City aged 18. Flanagan has earned numerous plaudits for his style of play since his breakthrough into the Liverpool first team in November 2013. On 4 June 2014, he made his England senior debut in the second half of a friendly against Ecuador in the United States.
Before getting promoted to Liverpool's senior team, he played in their youth program from 2004-2011. He was subsequently chosen as one of the reserve team to watch.
The World Cup winning former Brazil captain and full-back Cafu heralded Flanagan as his "successor", praising his "speed, strength and determination" and stating he "has everything required to be one of the best full-backs in the world".