Matthew G. Whitaker, the former acting attorney general and a loyalist to President Trump, is joining a cybersecurity firm as outside general counsel, one in a string of jobs he has taken on since leaving the administration, an official with the firm said on Sunday.

Mr. Whitaker’s role with the firm — PC Matic, which specializes in antivirus software — will be the second private sector job he has undertaken in the past few weeks. Gavin Smith, a spokesman for PC Matic, confirmed Mr. Whitaker’s position with the company.

Mr. Whitaker is also to be the managing director of Clout Public Affairs, a division of the political consulting firm Axiom Strategies. Axiom was founded by advisers to Senator Ted Cruz, Republican of Texas. Mr. Whitaker is also serving as of counsel to the law firm Graves Garrett, where he worked before joining the Trump administration.

Mr. Trump named Mr. Whitaker acting attorney general after Jeff Sessions was forced out after last fall’s midterm elections. Mr. Whitaker had served as Mr. Sessions’s chief of staff.