The website BuzzFeed dismissed one of its writers on Friday after finding 41 instances of “sentences or phrases copied word for word from other sites” among the 500 stories he had written, said the site’s editor in chief, Ben Smith.

The writer, Benny Johnson, 28, was the site’s viral politics editor and specialized in list-based articles about political news with headlines like “24 Delightful Inauguration Firsts.”

“Starting this Wednesday,” Mr. Smith wrote in an apology posted on the site, “Twitter users began pointing out instances in which a BuzzFeed writer, Benny Johnson, had lifted phrases and sentences from other websites.” When Mr. Johnson’s work was initially questioned, Mr. Smith stood by him. But after a review of his work, Mr. Smith said, “we had no choice other than letting him go.” The offending articles have been corrected and an editor’s note has been added to each, Mr. Smith said.

BuzzFeed has tried to mix established journalists — it recently hired Chris Hamby, who won the Pulitzer Prize for investigative reporting this year for work he did with the Center for Public Integrity — with writers who specialize in the lists and other popular online material that account for the bulk of the site’s traffic.