Thomas Mulcair said he didn't appoint Bruce Hyer to a shadow cabinet post because he thought the area MP was unreliable.
"He could not rely on me to park my brain at the door of the House of Commons. He could not rely on me to allow myself to be whipped by the party whip and the party leader and backroom party hacks," said Hyer on Thursday.
"If that's what he meant by unreliable, yes, I was not a mindless automaton for the party. I was not a customer sales rep for the party in Thunder Bay-Superior North," he added.
On Wednesday NDP leader Thomas Mulcair was in Thunder Bay on his cross-country affordability tour.
He told media that Hyer leaving the NDP in 2012 to sit as an Independent MP was not about the gun-registry vote, but that Hyer expressed frustration over not being given a shadow cabinet post.
"Frankly, I didn't find him very reliable and he's proven me right since then - he's not reliable," said Mulcair.
Hyer, who joined the Green Party in December, said despite leaving the NDP, he still represents the constituents of his riding no matter who they voted for.
Mulcair also said the NDP will reclaim Thunder Bay-Superior North in the 2015 federal election and many people who voted for the party are upset that Hyer crossed the floor.
"People voted for the NDP because they like our policies, they want us to be able to put those policies into force," he said.
"I guarantee we'll be taking that riding back."
But Hyer said that decision is in the voters' hands.
"I think Mr. Mulcair forgets that Thunder Bay-Superior North is not his riding or the NDP's riding. It's not my riding either. This belongs to the voters and constituents," he said.