Joe Arpaio, the longtime Phoenix-area sheriff whose headline-grabbing approach to immigration made him an ally of President Trump, will run in the 2018 Republican primary to replace Senator Jeff Flake, Republican from Arizona.

Arpaio, 85, made the bid official in an interview with the Washington Examiner.

‘‘I’m not here to get my name in the paper,’’ he said. ‘‘I get that everyday, anyway.’’

Arpaio, who has frequently talked about seeking higher office, said he decided to run as a ‘‘big supporter of President Trump’’ who would back the president wholeheartedly.

He is entering a primary against Kelli Ward, a former state senator also running as a Trump ally.

His decision may create an opening for Representative Martha McSally, Republican of Arizona, a Republican with more moderate views on immigration who is contemplating a bid for the seat and is backed by party leaders in Washington.

The former sheriff’s decision came as a surprise to some Democrats, who thought Arpaio’s career had ended in 2016. After 24 years as Maricopa County’s chief law enforcement officer, Arpaio was handily defeated by Democrat Paul Penzone.