Frank Merriam was born in a small community near Dubuque, Iowa. After graduating from Lenox College at Hopkinton in 1888, Merriam served as the principal of the Hopkinton's schools for two years and superintendent of schools at Postville for one year. He next became the editor of the Hopkinton Leader.
Merriam first entered politics in his home state of Iowa, serving as a member of the state’s House of Representatives and as State Auditor. In 1904, he moved to Muskogee, Oklahoma, where he owned and published the Muskogee Evening Times.
He moved to Long Beach California in 1910 with his first wife, Nellie. There he worked in the advertising department of the Long Beach Press. He served in the California Assembly for six terms, and served as speaker in the assembly for two terms. He was elected to the California Senate in 1928, where he served as presiding officer. In 1932, Merriam was elected lieutenant governor. On June 2, 1934, he assumed the role of acting governor upon the death of Governor James Rolph. As Governor, he waged a war against corrupt lobbyists and appointed a committee to investigate them. His arch-enemy was the notorious lobbyist Artie Samish, whose power was so great he scorned Merriam and called him "California's behind-the-scenes" governor.
Merriam's first wife died in 1931. He remarried Jessie Millisack Lipsie in 1936 and was the first governor to marry in office. The couple moved into the Governor's Mansion two days later. Merriam died at his Long Beach home on the evening of April 25, 1955.