He is a grandson of Charles Gavan Duffy, a PEI Liberal MLA and Speaker of the Legislative Assembly of Prince Edward Island.

In 1965, he served as news director at CKDH-FM in Amherst, Nova Scotia before heading to CFCF in Montreal as a lineup and assignment editor in 1969.

He became the lead CBC television reporter on Parliament Hill and covered the elections and most of the important federal stories of the Trudeau, Clark and Mulroney governments.

He covered the fall of South Vietnam in April 1975 and was one of the last journalists to leave before the arrival of North Vietnamese troops and Viet Cong insurgents.

Duffy was also a popular speaker at conferences, annual meetings and other events across Canada and, writer Stevie Cameron noted in her 1990 book Ottawa Inside Out, was probably the most-recognized journalist on Parliament Hill.

[4] It concluded that Duffy's decision to re-broadcast an earlier ATV Halifax broadcast of ‘false starts’ of an interview with then-Liberal leader Stephane Dion “was not fair, balanced, or even handed.”[5] The Panel also concluded that, during the same broadcast, Duffy “significantly misrepresented the view of one of the three members of his Panel...Liberal MP Geoff Regan.”[5] The panel thus concluded “that the consistent misrepresentation by host Mike Duffy of the MP’s point of view constituted an unfair and improper presentation of opinion or comment contrary to clause 6 of the CAB Code of Ethics.

"[5] In 1986, he won an ACTRA Award for live television reporting, for his coverage of the 1985 Turkish embassy attack in Ottawa by the Armenian Revolutionary Army.

[9] On December 22, 2008, Duffy was named a Prince Edward Island representative to the Senate on the advice of Prime Minister Stephen Harper, sitting as a Conservative.

[12] On February 28, 2013, the Senate Committee on the Internal Economy announced that Duffy, Pamela Wallin, Mac Harb, and Patrick Brazeau would be subject to a forensic audit to determine appropriateness of their expense claims.

Duffy's "free will" had been "overwhelmed" and he had "capitulated" as a result of the PMO's -- Prime Minister Stephen Harper's office, that is, -- "threatening efforts," the judge said.

The Superior Court judge said Duffy had been pressured by senior members of the Prime Minister's staff to admit to improper expense accounts when they were, in fact, legitimate, adding "the real deceit came from Harper's office.

"[20][21] Robert Fife, now the Globe and Mail's Ottawa bureau chief, won an award for his reporting on the so-called "Senate scandal."

On August 24, 2017, Duffy filed a lawsuit against the Senate and the Royal Canadian Mounted Police seeking damages of CA$8 million.