Steyn, a Canadian citizen, now resides mainly in New Hampshire in the United States. He is married with three children.

Steyn was born in Toronto. He was baptized a Catholic and later confirmed in the Anglican Church; he has stated that "the last Jewish female in my line was one of my paternal great-grandmothers" and that "both my grandmothers were Catholic". Steyn's great-aunt was artist Stella Steyn. Steyn was educated at the King Edward's School, Birmingham, in the United Kingdom. He left school in 1978 at 18 and worked as a disc-jockey before becoming musical theatre critic at the newly established The Independent in 1986. He was appointed film critic for The Spectator in 1992. After writing predominantly about the arts, Steyn's focus shifted to political commentary and moved to the conservative broadsheet The Daily Telegraph which stopped carrying his column in 2006.

Since then, he has written for a wide range of publications, including the Jerusalem Post, The Orange County Register, Chicago Sun-Times, National Review, The New York Sun, The Australian, Macleans, Irish Times, National Post, The Atlantic Monthly, Western Standard and New Criterion.

Steyn's website provides special commentary and access to many of his columns and other published work. He occasionally posts to the National Review Online group blog, The Corner.

Steyn's books include Broadway Babies Say Goodnight: Musicals Then and Now (a history of the musical theatre) and America Alone: The End of the World as We Know It, a New York Times bestseller. He has also published collections of his columns and his celebrity obituaries and profiles from The Atlantic.

Steyn occasionally fills in for Rush Limbaugh, a conservative talk show radio host.

Steyn is a visiting professor at Hillsdale College.

Steyn's writing draws supporters and detractors for content. His style was described by Robert Fulford as "bring[ing] to public affairs the dark comedy developed in the Theatre of the Absurd." Longtime editor and admirer Fulford also wrote, "Steyn, a self-styled 'right-wing bastard,' violates everyone's sense of good taste." According to Simon Mann, Steyn "gives succour to the maxim the pen is mightier than the sword, though he is not averse to employing the former to advocate use of the latter."

Susan Catto in Time noted his interest in controversy, "Instead of shying away from the appearance of conflict, Steyn positively revels in it." Canadian journalist Steve Burgess wrote "Steyn wields his rhetorical rapier with genuine skill" and that national disasters tended to cause Steyn "to display his inner wingnut."

Steyn frequently criticizes the institutional media.