WASHINGTON — Representative Phil Roe, Republican of Tennessee, announced on Friday that he would not seek a seventh term in 2020, becoming the first lawmaker this year to join the exodus of Republican lawmakers opting not to run for re-election as their party eyes another tough campaign cycle.

“As someone who practiced medicine for over 30 years, I said I would serve five or six terms because I never intended this job to be a second career,” Mr. Roe said in a statement. “After prayerful consideration, I have decided to retire at the end of the 116th Congress.”

An Army veteran and the top Republican on the Veterans Affairs Committee since 2017, Mr. Roe is now the 26th member of his caucus to leave before the next Congress because of retirement or ambitions for a different political office. Nine Democrats in the House have announced retirements for those reasons.

The stream of Republican departures comes amid deep frustration among the rank and file with the limitations of being in the minority in the House, which is entirely dominated by the majority. It has been hastened in part by term limits the party imposes on leadership positions, which have confronted many lawmakers with the unappealing prospect of waging another difficult re-election campaign in which the best-case scenario is hanging onto their job while losing a plum perch, and likely continuing to serve in the minority.