Nova Scotia MP Scott Brison described himself as a 'child of the Charter of Rights and Freedoms' as he entered Liberal leadership race. (CBC)

Describing himself as a defender of the environment, business innovation and socially progressive values, Nova Scotia MP Scott Brison has entered the race to become the next federal Liberal leader.

He becomes the sixth person to openly declare his candidacy in the race to replace Paul Martin, who stepped down shortly after the Liberals lost the Jan. 23 parliamentary election. The Liberal leadership convention is set for December.

"I will be presenting ideas throughout this campaign that can build a more economically competitive, socially progressive and environmentally responsible Canada," Brison told supporters as he made the announcement on Sunday in Wolfville, N.S.

He said policies that protect the environment could bring economic gains if the government supports clean-energy technologies.

Charter let me be 'open and honest about who I am': Brison

In 2004, Brison – then serving as public works minister in Martin's government – became the first cabinet minister to openly declare that he was gay. On Sunday, he described himself as a "child of the Charter of Rights and Freedoms."

He said he would defend the charter because "it has helped make Canada one of the most socially progressive societies anywhere in the world.

"It means I can serve the country I love as a member of Parliament, as a cabinet minister, even as a leader, while being open and honest about who I am as a person."

Brison vows to build more inclusive party

Brison said the Liberals need to attract more women to the party and help them become members of Parliament.

"I want to build a Canada where there are limitless opportunities and no glass ceilings, regardless of your gender, your sexual orientation, religion, or the colour of your skin."

Brison, 38, crossed the floor of the House of Commons to join the Liberals more than two years ago.

He was first elected as a Progressive Conservative MP for the Nova Scotia riding of Kings-Hants in 1997. But late in 2003, he left the party after it merged with the more right-leaning Canadian Alliance.

The other declared leadership candidates are Toronto MP Joe Volpe, former environment minister Stéphane Dion, former Harvard professor Michael Ignatieff, Toronto lawyer Martha Hall Findlay and MP Maurizio Bevilacqua, who represents the Ontario city of Vaughan.

Ontario's former NDP premier, Bob Rae, and Toronto MP Carolyn Bennett were expected to join the race on Monday.

Former Liberal finance minister Ralph Goodale, who had also been touted as a possible contender, said Friday that he was not planning to run.