Garven entered politics as a Republican and while the Democratic Party was split, he managed to get elected mayor in 1906.
His bid for a third term was stopped temporarily when he was defeated by Democrat John J. Cain in 1910.
In 1915, after Mayor Bert J. Daly stepped down there was a special election which Gaven won for the third time.
In July 1915, Garven's involvement in the Bayonne refinery strikes of 1915–1916 was somewhat compromised by his simultaneous employment as counsel for Standard Oil of New Jersey.
Garven suffered a stroke while visiting his daughters and died on October 19, 1938, in the Jersey City Medical Center.