The phrase "a vehement supporter" is correct and usable in written English.
It can be used to describe someone who strongly and passionately supports a particular cause, idea, or individual.
Example: "She is a vehement supporter of environmental conservation, often participating in rallies and campaigns."
Alternatives: "a passionate advocate" or "a strong proponent".
I am a vehement supporter of LGBT.
Chávez is a vehement supporter of Iran's nuclear ambitions and is a frequent visitor to Iran and Syria.
He served under Frank Weston, the Bishop of Zanzibar, a staunch Anglican with whom Keable clashed: Keable objected to Weston's unorthodox methods for training black African priests; Weston, a vehement supporter of these priests, saw prejudice in Keable's views.
Taylor was praised by writers who worked in a similar style, such as Elizabeth Bowen and Rosamond Lehmann; Kingsley Amis, perhaps her most vehement supporter, called her "one of the best English novelists born in this century".
In fact, even the most vehement supporters of relativism as a general theory make absolute judgments when they start talking about specific cases.
Despite record-setting rally turnouts of 28,000 and a grassroots effort manned by some of his most vocal and vehement supporters both on and offline in the Empire State, Sanders' momentum after eight straight primary victories failed to translate to the polls in New York on Tuesday.
The most vehement supporters of the Cominform were the Yugoslav communists under the leadership of Tito; therefore, Belgrade was selected as the seat of the organization.
The Huffington Post spent some time talking to pro-Sanders activists in Philadelphia to see what some of Bernie's more vehement supporters have to say.
The owner, I was told, was a vehement Qaddafi booster, whose sister was a notorious killer for the regime.
Adams's career as a champion of independence and a vehement critic of British imperial government began early.
He was a vehement critic of both German and Soviet historical crimes against Poland, and a strong supporter of countries such as Georgia.
