Lennon began his career at hometown club Leeds United, making his first-team debut in 2003 and becoming the youngest player to play in the Premier League at that time.

In 2008, Lennon won his first major honour, the League Cup, as Tottenham emerged victorious with a 2–1 win over London rivals Chelsea.

He scored nine goals in 77 appearances for Everton before joining fellow Premier League club Burnley in 2018 on a two-and-a-half-year deal for an undisclosed fee.

He made 55 appearances for the Lancashire club and scored one goal before departing on a free transfer to Kayserispor in Turkey in September 2020.

[6] He was first spotted by scouts when he was eight years old;[citation needed] his older brother Anthony played for Manchester United's youth team.

[10] Lennon had been featuring from the bench up until that point, but he soon took his chance when John Oster was sacked for bad behaviour, becoming a regular starter from then on.

[14] With Leeds' financial problems, Lennon was sold to Spurs for a heavily reduced fee, with a sell-on clause inserted into the deal.

[21] On 24 February 2008, Lennon won his first major career honour as Tottenham came from a goal down to defeat Chelsea 2–1 after extra time at Wembley Stadium in the 2008 League Cup Final.

[31] On 28 November 2010, he scored a last minute winner in a 2–1 victory against Liverpool at White Hart Lane after a Benoît Assou-Ekotto long ball.

[32] On 15 February 2011, Lennon went on a blistering run as Tottenham counter-attacked and then delivered a perfect pass to assist Peter Crouch in a 1–0 win over A.C. Milan at the San Siro in the Round of 16 of the Champions League.

[47][48] He began 2016 in a rich vein of form, scoring in a 1–1 draw at home to former club Tottenham,[49] and in three successive Everton wins in late January and early February.

[50] Lennon continued his scoring run in a 3–1 away win at Aston Villa[51] and he also netted in a 3–2 home loss to West Ham United on 5 March.

[52] However, this form proved to be short-lived as results for the team worsened and a poor end to the season led to the sacking of manager Roberto Martínez.

[53] The new season had a more frustrating feel as Lennon found himself well down the pecking order when new boss Ronald Koeman took charge of the club.

[69] Lennon also came on as a substitute during a 5–0 Euro 2008 qualifying victory over Andorra on 2 September 2006 and made an instant impact by assisting Peter Crouch's second goal after receiving the ball for the first time.

[73] This proved to be Lennon's last appearance for exactly two years as he was selected again by England on 28 March 2009, starting in a friendly match with Slovakia at Wembley Stadium.

[83] He won his final cap in a friendly against Brazil in February 2013, missing the following month's World Cup qualifiers due to injury.