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. He moved to Tottenham Hotspur in 2005 for £1 million, where he made 364 appearances across all competitions and scored 30 goals. In 2008, Lennon won his first major honour, the League Cup, as Tottenham emerged victorious with a 2–1 win over London rivals Chelsea.