"The league's council of [club] presidents approved an expansion of the competition to 18 clubs in the 2012/13 season," the LPFP said in a statement late on Monday.
The expansion would be achieved by allowing the bottom two teams this season to avoid relegation.
The decision, which provoked a heated exchange between club delegates, still needs to be ratified by the Portuguese Football Federation and Portugal's National Sports Council. Some of the clubs which voted against the proposal said they would challenge the measure.
The LPFP also delegated president Mario Figueiredo with the task of preparing a complaint to the European Union about the current TV rights bargaining model that privileges bigger clubs.
"This was an historic day, we managed to gather support for a structural question and an eventual complaint to end the monopoly of TV rights," Figueiredo said.
He wants the LPFP to be the single negotiator of TV rights for all of the Portuguese Premier League instead of the current model whereby TV contracts are negotiated on a club-by-club basis.
This means that in Portugal, as well as in neighboring Spain, the bulk of broadcast rights revenues are dominated by bigger clubs, with half of the revenues going to the so-called "big three" of Benfica, Sporting and Porto.
Benfica and Porto did not back the move to collective selling.
Yearly revenues from TV rights are estimated at around 75 million euros - a modest sum compared with the fees earned by clubs in larger European leagues in England, Spain, Italy, Germany and France.
Benfica rated 21st internationally in terms of football club income in 2010/11, according to a recent survey by British business firm Deloitte.
