Councillor Cherise Welch, who represents Harmans Water and Crown Wood, has joined the Liberal Democrats after previously serving as an independent.
Welch, elected to Bracknell Forest Council in 2023, said she will keep focusing on health and education services, plus tackling littering and fly-tipping.
"I'm delighted to be joining the Liberal Democrats. I got into politics to stand up for my local community, and I've found a party that shares my values and my priorities.
"I'll be fighting to protect health and education services for local people, and to look after our environment by tackling littering and fly-tipping."
The Bracknell Forest Liberal Democrats said Cllr Welch had previously served as a school governor and had been involved in local campaigns against litter and fly-tipping.
Councillor Mike Forster, leader of the Liberal Democrat group, said: "She is a real community champion who has worked tirelessly for her residents, and her dedication to protecting our environment and championing local services is exactly what Liberal Democrats stand for."
The move increases the Liberal Democrat group on the 41-seat Bracknell Forest Council from seven councillors to eight.
The council's most recent political balance recorded 18 Labour councillors and 10 Conservatives, with Labour remaining the largest group. All 41 borough seats will be contested at the next all-out elections in May 2027.
Katie French, Local Democracy Reporter
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