In 1940 he was appointed to succeed Jim Farley as Postmaster General of the United States, in which position he served until 1945. In 1946 he was appointed by President Truman as alternate delegate to the first United Nations General Assembly session in London. He returned to his business interests in N.Y. as director of W. R. Grace & Co. and the Grace National Bank of New York.

Frank C. Walker was born on 30 May 1886 to Ellen and David Walker in Plymouth, Pennsylvania. He was the eleventh of fourteen children. Ellen Walker ran a general store in Plymouth during Frank's earliest years while her husband tried prospecting in Montana. By 1890, the family had enough money to settle together in the growing mining town of Butte, Montana, where Frank spent most of his youth.

The Walkers initially prospered in Montana. As the owner of small mines or as the superintendent of large mines, David Walker was able to provide for his family until falling ill in 1901. At age fifteen, Frank Walker dropped out of school and worked for two years as a tool carrier in the mines to help support the family.

Family finances improved and Frank was able to continue his education. He spent three years in preparatory and collegiate courses at Gonzaga University in Spokane, Washington. After graduating from Gonzaga in 1906, he enrolled in the University of Notre Dame Law School and began an affiliation with that university which lasted throughout his life. Walker graduated from Notre Dame in 1909 and returned to Butte to commence his legal career. He first served as Assistant County Attorney until 1912 when he was elected to the Montana state legislature. Walker served only one term in the legislature before leaving to establish a law partnership with his brother, Thomas.

In 1914, Walker's attention was turned from his career to other concerns. In November he married Hallie Boucher, daughter of a Butte merchant. The year of Walker's marriage was also the start of World War I, and he served as a first lieutenant, arriving in France just one week before the armistice. After the war, the Walkers saw the birth of a son, Thomas, born in 1921, and a daughter, Laura, born in 1924.

Following the birth of his daughter, Walker left his law partnership and Butte to join his uncle, M.E. Comerford, in the successful Comerford Amusement Enterprises in New York City. Walker began as general counsel to the chain of Comerford theaters; by 1935 he was the chief operating officer. Walker's move to New York was important not only for his legal career but also for his future in politics. Exposure to political corruption and the struggles of labor in Butte's mining industry had provided him with firsthand knowledge of the need for progressive reforms. Now association with the progressive governor of New York, Franklin D. Roosevelt, confirmed Walker in those political beliefs.

Walker first met Roosevelt in 1920 when FDR was running for vice-president and was on a campaign trip that took him to Butte. But Walker's friendship and political alliance with the future president really began during Roosevelt's gubernatorial reelection campaign in 1930. By 1932 Walker was part of the inner circle of Roosevelt's emerging campaign for the presidency. A member of FDR's pre-convention committee, Walker was one of the principal donors to the early campaign. After FDR's close convention victory in Chicago, Walker was named Democratic National Committee (DNC) treasurer in August 1932.

With Roosevelt's election to the presidency in November 1932, Walker played an important role in the organization of the new administration. He advised Roosevelt on cabinet appointments as well as lower level positions. Initially uninterested in a post for himself, by the summer of 1933 Walker had been persuaded to head the Executive Council, a new body established that July to coordinate the administration's activities with appropriate governmental agencies. Comprised of cabinet members and agency heads, the Executive Council met weekly with the president.

Walker's role as coordinator of federal departments and agencies was expanded again when in November he was named director of the National Emergency Council (NEC). The NEC functioned much like the Executive Council, but it had fewer members, was national in scope, and concerned itself only with New Deal programs. Walker ran both councils from the same office. By October 1934, the two councils merged into one, keeping the name NEC.

Much of Walker's work with the NEC was with subsidiary governmental units. At his direction a government manual was prepared outlining all government departments and agencies. The United States Information Service was formed to disseminate information to the general public about the function and personnel of all government departments and agencies. Walker also helped plan and achieve passage of the National Housing Act, an attempt to encourage renovation of existing housing stock as well as the creation of new housing.

After the National Housing Act was signed in June 1934, Walker took a leave of absence from the government to concentrate on family business. He had never actually given up his work with Comerford Enterprises, commuting between New York and Washington several days each week. But Walker's plan to work only in one city was temporarily postponed when the following April he acceded to a request from Roosevelt to head the NEC's Division of Applications and Information (DAI), an office designed to review, rout, and report to the press on all applications to the four billion dollar Works Relief Program.

Walker spent an additional eight months dividing his time between the government and his private interests, but when the illness of his uncle, M.E. Comerford, and the death of his cousin, M.B. Comerford, gave him control of Comerford Enterprises, he needed to devote more of his time to business affairs. With his final resignation from the NEC, Walker concentrated his efforts on promotional activities for his theaters, in particular a quiz contest for moviegoers called "Motion Pictures' Greatest Year."