Born in Highgate Center in Franklin County, Vermont, he attended public schools, Bakersfield Academy1, and then the University of Vermont, from which he graduated in 1899. He then studied law and entered practice in 1902. In 1904 he was appointed State's attorney of Franklin County, a position he held for two years.
In his first few years in politics, he served in a number of roles, including chairman of the Vermont Republican State Convention in 1908, Mayor of St. Albans in 1909, a delegate to the Congress of the Mint in 1912, and a member of the United States Court for China in 1917. During this period, he also served as a United States commissioner (from 1907 to 1915).
His rising prominence led to his appointment as a trustee of the University of Vermont in 1914, a position he would retain until 1941.
He also served as a special counsel for Vermont in a dispute over the exact border between Vermont and the neighboring state of New Hampshire from 1925 to 1937.
He was elected to the Senate on March 31, 1931, in a special election called upon the death of former Senator Frank L. Greene, and took his seat the next day. He went on to win re-election twice (in 1934 and 1940). In the Senate, Austin championed internationalist causes--standing with President Franklin D. Roosevelt on issues such as neutrality and Lend-Lease. He resigned on August 2, 1946, near the end of his last term, in order to accept appointment as the U.S. Ambassador to the United Nations, a position he held until January 25, 1953, when he retired to Burlington.
He was a member of a number of organizations and societies, professional and otherwise, including the American Bar Association, the American Judicature Society, the Loyal Legion, the Society of the Cincinnati, the Freemasons, the Shriners, the Odd Fellows, the Rotary Club, and Kappa Sigma. In religion he was a Congregationalist Christian. Austin received an LL.D. from Bates College in 1947. Austin is memorialized in a marble tablet in the Vermont State House's hall of Inscriptions at Montpelier, Vermont.