"fervent follower" is correct and usable in written English.
You can use it to describe a person who is very devoted and passionate about a particular entity, usually someone or something they admire or support. For example: Jack was a fervent follower of the local baseball team and attended every home game.
Ewart Shadoff's husband studied broadcasting at Syracuse, and he remains a fervent follower of his alma mater's basketball team.
A key figure of Hitler's inner circle was Joseph Goebbels, minister of propaganda and a fervent follower whom Hitler selected to succeed him as chancellor.
She has become a fervent follower of the Concourse's Bronx Museum of the Arts and also makes her way farther south to the galleries in the small art colony in an industrial neighborhood along Bruckner Boulevard.
And despite his well-known reverence for Jefferson Davis and his close ties to the rancid Council of Conservative Citizens, the junior senator from Mississippi insists he is now a fervent follower of the teachings of Martin Luther King.
As a fervent follower of Hōnen, Shinran adopted his teaching of the "exclusive nembutsu" (senju nembutsu): invoking the name of Amida Buddha is the sole practice assuring enlightenment in the Pure Land.
These rumors seemed not so incredible because the emperor had become a fervent follower of Chan Buddhism in the late 1650s, even letting monks move into the imperial palace.
Still, the embattled Yemeni president has his fervent followers, especially in the old city.
Now Trump and his most fervent followers are attacking the FBI for anti-Trump bias.
Fervent followers of Islam were horrified that infidel troops had been brought into the land of Mecca and Medina.
Several of the most fervent followers of the campaign say that their habits were formed in childhood.
His most fervent followers were in England, where his fawning devotee and erstwhile editor Vladimir Grigoryevich Chertkov lived during a period of exile.
