Robert M. Riddle (August 17, 1812 – December 18, 1858) was a newspaperman, postmaster and politician who served as Mayor of Pittsburgh from 1853 to 1854. Robert M. Riddle was born in 1812, the son of Judge James Riddle. He entered the mercantile trade in Pittsburgh in the firm of Riddle and Forsyth, and subsequently engaged in the banking business in Philadelphia. While at the helm of the Journal, Riddle was elected on the Whig ticket as Mayor of Pittsburgh. He was not renominated at the end of his single-year term.