The 85-year-old soap star, who performed with the group at a Christmas concert at the Brighton Dome last year, wrote to the chairman of the chorus to accept the role.
The news coincides with the announcement that Brown's EastEnders long-standing character of Dot Branning will return to Albert Square in January.
Of her new role in Brighton, Brown said: "I am very supportive of the charitable work the Chorus is involved with, and may I take the opportunity to wish the best to your members with their most conscientious endeavours moving forward."
Adam Betteridge, a trustee for the Chorus, said: "We are very excited that June has recognised the important work that Brighton Gay Men's Chorus carries out in our community and agreed to become our Patron.
"We believe that June's support will help bring public attention to our charitable activities and objectives at a much wider level, and we are most appreciative of her very kind support."