Barnet F.C.
On 21 May 2019, Brennan was named as the new manager of National League South side Wealdstone, with Stuart Maynard as his assistant manager. In the shortened 2019-20 season, Brennan led the club to automatic promotion to the National League, as champions of the National League South. In December 2020, he turned down an approach from Barnet F.C. to be their manager. On 2 February 2021, Brennan resigned from his role at Wealdstone, with Maynard remaining at the club.