WASHINGTON — A former investigator for Republicans on the House Select Committee on Benghazi filed a lawsuit against the panel and its chairman on Monday, contending that they had illegally fired and defamed him.

The former investigator, Bradley F. Podliska, said in the suit that he had been dismissed because he left the committee for several weeks to fulfill his duties as an Air Force reservist. It also said that after it was revealed in October that Mr. Podliska planned to file a complaint against the committee, the chairman, Representative Trey Gowdy, Republican of South Carolina, made false statements about Mr. Podliska to the news media that damaged his reputation.

The lawsuit, filed in federal court here, says committee staff members “singled out” Mr. Podliska because he was unwilling to go along with the committee’s focus on the State Department and former Secretary of State Hillary Rodham Clinton.

Mr. Podliska’s suit seeks his reinstatement as a committee investigator, compensation for lost wages and other damages. He is also seeking “a permanent injunction barring Chairman Gowdy from repeating false, defamatory and injurious statements” about him.