[4] Born in Kingston upon Thames, London,[2] Lewington made his Wimbledon first team debut on 5 April 2003, coming on as a last-minute substitute for Alex Tapp in a 4–2 First Division defeat to Sheffield Wednesday at Hillsborough, his only appearance of the season.

[5] On 1 November 2003, he made his first start, in a 2–1 win over Bradford City at the National Hockey Stadium, their first victory in Milton Keynes.

The 2–2 draw with Rotherham United at the New York Stadium on 26 April 2014 saw Lewington make his 500th appearance for Milton Keynes Dons in all competitions.

To celebrate his 500th appearance for the club, supporters of Milton Keynes Dons got together for the last home game of the season against Leyton Orient, and wore as much orange as possible (due to Lewington's hair colour).

On 3 May 2015, Lewington scored twice and assisted two further goals as the Dons defeated Yeovil Town 5–1 on the final day of the season to earn their first promotion to the Championship.

[11] On 20 May 2014, Milton Keynes Dons announced a testimonial match against Nottingham Forest would be played in honour of Lewington's ten years of service for the club.

[20] On 3 August 2021, just four days before the beginning of the 2021–22 season, MK Dons announced Lewington would take over as interim caretaker manager following the departure of Russell Martin, whilst the club sought a permanent replacement.

[28] On 19 September 2024, Lewington became caretaker head coach of the club for a third time following the departure of Mike Williamson to Carlisle United.