(CNN) Rep. Mac Thornberry on Monday became the sixth Texas Republican to announce plans to head for the exits of Capitol Hill, saying in a statement that he will not seek reelection in 2020.

"It has been a great honor to serve the people of the 13th District of Texas as their congressman for the last 25 years," he wrote. "We are reminded, however, that 'for everything there is a season,' and I believe that the time has come for a change. Therefore, this is my last term in the U.S. House of Representatives."

Thornberry, the top Republican on the House Armed Services Committee, has served in Congress since he was first elected in 1994. Texas's 13th congressional district is considered a safe Republican seat: In 2018, Thornberry won reelection by nearly 65 points.

His departure isn't entirely shocking — in recent weeks he had been noncommittal about running again, saying in September that "people should not make too much of the fact that folks who have been in a while or have put limits on themselves, how long they would serve, have decided to do something else."

He was also set to reach the term limit for the Armed Services Committee next year. Since 1994, House Republicans have limited committee chairmanships to six years, including time spent as ranking member in the minority, unless members obtain a waiver from the Republican Steering Committee. Democrats don't have the same rule.

Read More