Answer:
Gerald R. Ford. Ford was selected and confirmed as the vice President on December 6, 1973, while he was a US Congressman, after the resignation of Vice president Spiro T. Agnew. Ford then became President on August 9, 1974 with the resignation of President Richard M. Nixon.
(Ford ran for reelection but was defeated by Jimmy Carter in 1976, so he was never elected President or vice president.)