Chris Davies and Gary Hopkins also say by creating Knowle Community Party they can avoid ‘bickering’ between parties on subjects like the mayoral referendum next year.
The pair have represented the Knowle ward as Lib Dem councillors for 18 and 19 years respectively.
And their move alters the political make-up at City Hall, with their old party now reduced to six councillors.
The move was announced in a statement put through residents’ letterboxes this week.
Speaking to BristolWorld, Councillor Hopkins said: “We were elected under the slogan ‘Chris and Gary Working for Knowle’ back in May - and we, as a pair, don’t want anything getting in the way of looking after the residents.
“We also have the mayoral referendum next year, an issue we feel we would be a better position to campaign on without being part of one of the four political parties.
“We don’t want to be involved in a cross-party bickering on such an important issue.”
Both councillors are strong supporters of dropping the mayoral role, a position they say has not served the people of Knowle.
Calls to keep open Jubilee swimming pool and protect Brislington Meadows from housing have not been prioritised enough under a ‘centralised’ mayoral system, said Councillor Hopkins.
He said his new party aims to push for the opening of a new secondary school in Daventry Road, secure investment for Broadwalk Shopping Centre and protect the Jubilee Pool.
He also said removing the mayoral system was a key aim for the pair.
He added: “The mayoral position has centralised things in Bristol - any big project they are interested in and the local needs are completely forgotten.
“We want to go in the opposite direction.”
Councillor Andrew Brown, of the Lib Dem group at the council, said because the pair had not been attending group meeting for a number of months, their departure was not a surprise.
He added: “Although it is disappointing, it has not come as a huge shock.
“We look to the future and we, ourselves, will start preparing for the mayoral referendum campaign as well as continuing to stand up for the residents of Knowle and other areas of the city.”