Bentley, the only child of Alvin M. Bentley, Jr., and Helen Webb Bentley, was born in Portland, Maine only three months before his father died serving in France during World War I. Although fatherless, Bentley was heir to a family fortune, from his grandfather who founded the Owosso Manufacturing Company.

He graduated from Southern Pines High School, Southern Pines, North Carolina, in 1934 and from the Asheville Prep School, Asheville, North Carolina, in 1936. He received a B.A. from the University of Michigan, Ann Arbor, Michigan in 1940 and attended Turner’s Diplomatic School, Washington, D.C., to qualify for diplomatic service. He served as vice consul and secretary with the United States Foreign Service, serving in Mexico (1942-1944), Colombia (1945-1946), Hungary (1947-1949), and Italy (1949-1950). He returned to Washington, D.C., on March 15, 1950, for work in the State Department. Disagreeing with the Truman administration's foreign policy, Bentley resigned from the diplomatic service in 1950 and returned to live in Owosso, Michigan. He was a delegate to Republican State conventions in 1950, 1951, and 1952. He was vice president of Lake Huron Broadcasting Company, Saginaw, Michigan, starting in 1952, and the director of Mitchell-Bentley Corporation.

In 1952, Bentley defeated the incumbent Republican U.S. Representative Fred L. Crawford in the primary election for Michigan's 8th District and went on to win in the general election. Bentley was elected to the Eighty-third and to the three succeeding Congresses, serving from January 3, 1953 to January 3, 1961. He was not a candidate for re-nomination in 1960, instead running for a seat in the United States Senate and losing to Democratic incumbent Patrick V. McNamara in the general elections.

Bentley was one of five Representatives shot on March 1, 1954, in the U.S. Capitol shooting incident when four Puerto Rican nationalists opened fire from the visitors' balcony into the chamber of the United States House of Representatives. Bentley was shot in the chest.

From 1961 to 1962, Bentley was a delegate from the 15th Senatorial District to the Michigan State Constitutional Convention, which produced the Michigan state constitution adopted in 1963. In 1962, Bentley again ran for the U.S. House for a one-term, at-large seat created as a result of the 1960 United States Census, but he lost in the general election to Democrat Neil Staebler. He continued public service by receiving appointments to education-related positions in the state. Also, after leaving Congress in 1961, he had returned to the University of Michigan as a graduate student in the History department. While continuing to maintain offices in Washington, D.C., Bentley commuted by air to Ann Arbor to attend classes. He received a M.A. degree in 1963. In 1966, while pursuing a doctoral degree, Governor George W. Romney appointed him to the board of regents of the University of Michigan, a position he held at the time of his death while on vacation in Tucson, Arizona.

He is interred in Oak Hill Cemetery in Owosso, Michigan.