Richard Corcoran, the speaker of the Florida House, announced Tuesday evening that he had fired Mr. Kelly at Mr. Harrison’s request. Mr. Harrison confirmed the firing in his own statement on Twitter, shortly after voting against consideration of a bill that would have banned assault rifles like the one used in the Stoneman Douglas shooting. (A motion to take up debate on the bill failed, 36 to 71, on a party-line vote.)

“I am appalled at and strongly denounce his comments about the Parkland students,” Mr. Harrison, a Republican representing a district north of Tampa, tweeted, adding that Mr. Kelly had made his remarks “without my knowledge.” Mr. Harrison did not immediately respond to a voice mail message at his Tallahassee office, and the voice mail at his district office was full.

In a tweet confirming his firing, Mr. Kelly said that he had “made a mistake whereas I tried to inform a reporter of information relating to his story regarding a school shooting,” and that Mr. Harrison should not “be held responsible for my error in judgement.”

Mr. Kelly did not respond to a Twitter message asking whether he stood by his claim that the students were actors, and whether his “error in judgment” was in believing that or simply in sharing the belief with a reporter. By 8:30 p.m. on Tuesday, he had made all his tweets private.

Earlier in the day, as students boarded a bus to lobby state lawmakers in Tallahassee, Cameron Kasky, a 17-year-old junior at Stoneman Douglas, urged his classmates not to let conspiracy theories distract them.