“My decision to sit as an Independent was a response to the way the major parties limited true representation of my constituents by demanding lockstep discipline,” Hyer said in a statement.
“This mindless solidarity prevents cooperation and compromise, meaningful policy discussion and finding productive solutions for Canadians.”
Hyer, a longtime advocate of democratic reform, made the announcement with Green Party Leader Elizabeth May at his side.
Hyer left the NDP caucus on April 23, 2012, after party discipline required New Democrat MPs to support the long-gun registry, something the MP for Thunder Bay–Superior North said he could not do.
The NDP had previously disciplined the Ontario MP and NDP MP John Rafferty for siding with the Conservatives during a vote to dismantle to gun registry.
In an interview, May told Julie Van Dusen of CBC News that "the policies of the Green Party oppose the idea that political party affiliation should trump your commitment to your constituents."
"[Hyer] has a long history as someone who has been a committed environmentalist, conservationist…he has a very strong 'green' track record," she said.
May said she and Hyer had a lot of time to talk this past year and a half as the two are seated next to each other in the Commons.
The NDP called on Hyer to resign his seat immediately and run again in a byelection, saying he is betraying his constituents by joining a party they did not vote for in the last federal election.
"Hyer has broken faith with the voters. We are calling on him to do the right thing, the honourable thing, and immediately resign his seat and give the voters of Thunder Bay-Superior North a real choice in a by-election," NDP ethics critic Charlie Angus said in a written statement.
Angus said Hyer really left the NDP caucus because he was not given a role in the party's shadow cabinet.