Dean James Gary Brennan (born 17 June 1980) is an Irish football manager who is head coach of National League club Barnet.

As a player he was a winger / attacking midfielder who played professionally for Sheffield Wednesday, Bohemians and Luton Town before spending the remainder of his career in the English non-league.

Brennan began his footballing career at Sheffield Wednesday but despite impressing at youth and reserve levels, he never made a first team appearance for the Owls.

[3] Luton would prove to be his last taste of League football as he drifted around the non-League scene with spells at Stevenage, Grays Athletic, Lewes, AFC Wimbledon, Cambridge City, Chesham United and Hemel Hempstead Town in the following years.

After a disastrous start to their first season in the Conference South league, Hemel improved and eventually finished in a creditable 9th position, also reaching the First Round of the FA Cup where they lost at Bury 3–1.

The 2015–16 National League South season saw Brennan's Hemel narrowly miss out on the playoffs as Whitehawk pipped them on the final day to fifth place.

However, on 16 March 2019, following a breakdown in relations with a club director over player liaison and team strategy, Brennan and Maynard re-evaluated their position and resigned after just five games in charge.