Martin's military career spanned forty years, dovetailing with that of his West Point classmate, General John J. Pershing. Martin served under Pershing during World War I and from 1922 to 1924 as the U.S. Army Assistant Chief of Staff. Martin's honors included the Distinguished Service Medal and two citations for bravery in action. He commanded the famous Blackhawk Division and the Fifth Corps in the Argonne during World War I. His career included service during the Spanish-American War, the Philippine-American War, the Boxer Rebellion in China, and as commander of the Panama Canal Department from 1925-27. Martin retired with the rank of major general on his sixty-fourth birthday in 1927.

Martin retired to Portland, Oregon, with his wife, the former Louise J. Hughes, daughter of a prominent Portland attorney. The couple had met when, as a lieutenant, Martin was on his first assignment at Vancouver Barracks. They were married in 1897.

With his retirement from military life, Martin embarked on his second career in politics. From March 4, 1931, to Jan. 3, 1935 he served as a conservative Democratic Representative to Congress from Oregon's nominally Republican Third Congressional District.

In 1934, Martin was elected as Oregon's governor. This was a time of intense labor turmoil and the middle of the Great Depression. Governor Martin earned a reputation for putting state finances back on a sound basis. In fact, even when the Depression eased, he opposed full restoration of wage levels for state employees, who had suffered a fifty percent pay cut during the Depression.

Major issues dealt with during Governor Martin's administration were economic recovery from the Great Depression, reconstruction of the State Capital, the planning and construction of Bonneville Dam, as well as development of statewide port and highway infrastructures. Labor issues were significant particularly in the timber and shipping industries.

An obituary in Portland's The Oregonian summarized his labor policies: "His attacks against labor policies of the New Deal and his fight to have part of Bonneville Dam power turned over to industry brought him criticism from labor and farm organizations." Martin grew in his vocal opposition to Roosevelt's New Deal, especially to the National Labor Relations Board (NLRB) and the President's labor policy. In 1937 the NLRB failed to settle a jurisdictional dispute between the Congress of Industrial Organizations (CIO) and the American Federation of Labor (AFL) that had closed all Portland sawmills. Martin stepped in and held his own elections, which led to the reopening of the mills. He made himself the enemy of what many saw as corrupt labor leaders, particularly by his appointment of Assistant Attorney General Ralph E. Moody to prosecute many union people accused of arson and assault.

He was often quoted for his rephrasing of President Roosevelt's famous pronouncement on fear. Martin said, "We have nothing to fear from the future except our own foolishness and slothfulness." His criticism of President Roosevelt cost Martin a bitterly contested bid for the Democratic Party's Oregon gubernatorial nomination in 1938.

The nomination lost, Martin retired from active politics to his Portland home. He died on Sept. 22, 1946. Interment was at Riverview Cemetery in Portland.