Maynard-Brewer began his career in the academy at Australian club ECU Joondalup, before signing for Charlton Athletic in 2015, where he is contracted until the end of the 2022–23 season.[4][5] On 13 November 2018, Maynard-Brewer made his debut for Charlton in a 1–0 EFL Trophy loss against Swansea City U21s.[6]
On 5 August 2019, Maynard-Brewer joined Dulwich Hamlet on a 28-day emergency loan,[9] and the following January he joined Dover Athletic.[10]
Maynard-Brewer joined Ross County on a season-long loan in August 2021.[11] Ahead of the 2022–23 season, Maynard-Brewer joined recently-relegated League Two club Gillingham on another season-long loan, Charlton holding the option to recall him.[12][13] In July 2022 he suffered a dislocated shoulder in a pre-season friendly against his former side Dover Athletic, keeping him out of action for several months.[14] He returned to action for Charlton's U21s side in a 2–0 loss to Bristol City's U21s on 1 November 2022.[15] Maynard-Brewer was recalled from his loan on 17 November 2022 without making a competitive first-team appearance for Gillingham.[16]