His most recent appointment was the assistant manager at Cambridge United During his playing career, he appeared professionally (predominantly as a midfielder) for six different clubs.

Waddock was named by Jack Charlton in the squad for the 1990 FIFA World Cup, but having travelled to the pre-tournament camp in Malta, he was dropped at the last minute in favour of Alan McLoughlin, seen as better cover for players nursing injuries.

He left QPR for Charleroi in Belgium for three years between 1987 and 1989, making 40 appearances and scoring one goal, before returning to London with Millwall.

[5] On 20 September 2006, after a poor set of results had left QPR bottom of the table, Waddock was replaced by John Gregory.

[7] Waddock won his first trophy on 3 April 2008, when Aldershot Town beat Rushden & Diamonds 4–3 on penalties in the Conference League Cup.

[11] Despite a turn in form, and a large turnover of players towards the end of the season, Waddock was unable to prevent Wycombe Wanderers' relegation to League Two.

Waddock again added to his squad in the summer by signing Nikki Bull, Andy Sandell and Dave Winfield, who he had previously managed, whilst at Aldershot Town.

At the start of 2011, he captured Scott Donnelly on a season long loan, who he previously managed at both Queens Park Rangers and Aldershot Town.

On 22 March 2014, Waddock was appointed as Head Coach of Oxford United, replacing caretaker manager Mickey Lewis.

[17] On 13 April 2015, Waddock was named as temporary manager for the last four games of the 2014–15 season after Andy Awford left the position by mutual consent.