Mulcair spoke about his friendship with the late, former Canadian finance minister, and offered his condolences to Flaherty's family.
(*Below, Prime Minister Stephen Harper also addresses Flaherty's death.)
"Catherine and I want to express to Christine Elliott (Flaherty's wife) our profound sadness at the departure of our friend," Mulcair told reporters on Thursday. "All his colleagues here in the House of Commons share in that loss. He's a good person. I had a chance to know him before being in federal politics and he's a strong, touch character."
"We're very, very sad for the loss of a great Canadian... an extraordinarily dedicated public servant. He will be greatly missed by all of us."
Video: The Canadian Press