He served for three years as a U.S. Representative from Vermont and was the Republican nominee for United States Senator in 1974, losing narrowly to Patrick Leahy.

[2] Mallary operated a dairy farm in Fairlee, Vermont from 1950 to 1970, where he was subsequently elected chairman of the town Board of Selectmen, serving from 1951 to 1953.

In the House Mallary was recognized as one of the "Young Turks," the group of legislators who crossed party lines to advocate for progressive policies and the modernizing of Vermont's state government.

Mallary served as Chairman of the Vermont Legislative Council from 1965 to 1967, and as a delegate to the 1968 Republican National Convention which nominated Richard M. Nixon for President.

[8] Mallary was elected as a Republican to the Ninety-second Congress, filling the vacancy caused when Robert T. Stafford resigned to accept appointment to the United States Senate.

He was, as the Republican nominee, an unsuccessful candidate for election to the United States Senate in 1974, narrowly losing to Patrick Leahy by a margin of 49.5%–46.4%.

[11][12] In 2003, Mallary served as Vermont's tax commissioner, an appointed sub-cabinet position, in the administration of Republican Governor Jim Douglas.