The Alberta Party and the Green Party have also nominated her as their candidate, but she will be listed on the ballot as a Liberal.
Blakeman called the move an historic first step toward unifying progressive voters in the province.
"I believe the joining of forces by the three parties is essential to provide Alberta voters a centrist alternative to the (Progressive) Conservatives," she said Friday.
Blakeman said she plans to put the logos of all three parties on her campaign literature.
Alberta Liberal Leader David Swann said he shares Blakeman's concerns about the need for progressive parties to co-operate.
He called her move a symbolic gesture that will give all progressive Albertans hope. He noted the looming provincial election expected to be called this spring is too close for the Liberals to do more.
"I support Laurie and I thank her for her decision to run under the Liberal banner while uniting with others," he said.
Alberta Party Leader Greg Clark said he was "thrilled" with Blakeman's decision.
Green Party Leader Janet Keeping said she admires Blakeman's determination to do politics differently.
"More candidates should do the same," Keeping said. "Albertans desperately need brave, creative and progressive people in the legislature, and Greens enthusiastically endorse Laurie as our candidate in Edmonton-Centre."
The Alberta Party and the Green Party don't hold any seats in the legislature.
Blakeman has represented the riding since 1997, winning five straight elections, each with more than 40 per cent of the vote.
The NDP candidate in the constituency is David Shepherd. The Progressive Conservatives are to nominate a candidate March 28.
The governing Progressive Conservatives currently hold 70 seats in the 87-seat legislature.
The Wildrose and Alberta Liberals have five each, the Alberta NDP has four. There is one Independent and two seats are vacant.
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