A summer signing for the U's in 2016, Brennan started his career in non-league, but his performances for Dorchester soon caught Brighton's attention and he joined the Seagulls in January 2012.
He enjoyed loan spells at Chesterfield, AFC Wimbledon and Northampton Town, before joining Gillingham in June 2014 for an undisclosed fee, signing a two year contract.
It was with the Gills that he really established himself and he played 79 times in two seasons, scoring four goals. That included 36 appearances last season, where the Gills were flying high for most of the campaign.
He has made a big impression in his time at the U’s, scoring frequently from a left wingback position and setting up a number of goals for his teammates.