At the age of 21, Sadler entered coaching, joining Newcastle United in 2001. During his time at the club, Sadler was appointed
reserve team manager, helping the side to win the
Northumberland Senior Cup. A short spell at
Norwich City under
Glenn Roeder was followed by a return to
North East England, where he was assistant manager at Blyth Spartans,
Team Northumbria, and
Gateshead. Sadler later joined
Plymouth Argyle, eventually becoming first team coach under manager
Peter Reid. In August 2011, Sadler joined
Manchester City as under-18 coach. Following two years at Manchester City, Sadler took up a coaching role at Ukrainian club
Tavriya Simferopol. In 2023, following the sacking of
Brendan Rodgers, Sadler was once again appointed as
joint-caretaker manager with Stowell. They managed the team in a 2–1 home defeat against
Aston Villa on 4 April. After the arrival of the new manager
Enzo Maresca, he left the club on 30 June.
Northern Ireland On 28 August 2021, Sadler joined the backroom staff of the Northern Ireland national team in conjunction with his coaching role at Leicester City.
Celtic Sadler was appointed first-team coach at
Scottish Premiership club
Celtic on 31 December 2023, reuniting with manager Brendan Rodgers. He left the club on 29 October 2025, following the departure of Rodgers. ==Managerial statistics==