Brill joins the O’s coaching staff having spent the second half of last season at Sky Bet League Two side Colchester United.
The 31-year-old arrives with a wealth of playing experience, having progressed through the Centre of Excellence at Luton Town.
After making his professional debut in 2003, Brill went on to make a total of 97 appearances for the Kenilworth Road outfit prior to leaving at the end of the 2008-09 season after helping the Hatters win the Football League Trophy.
Spells at Oldham Athletic and Barnet then followed for Brill, before he returned to Luton ahead of the 2012-13 campaign in which he made a further seven appearances.
Brill made the switch to Scotland in July 2013 to join Inverness Caledonian Thistle, and enjoyed three years at the Caledonian Stadium.
Last summer saw Brill sign for fellow Scottish Premier League side Motherwell, prior to returning to England in January 2017 in order to sign for Colchester United until the end of the season.