Ottar Dahl (5 January 1924 – 4 April 2011) was a Norwegian historian and historiographer.
Dahl was born in Nannestad. He took the dr. philos. degree in 1957, worked at the University of Oslo as a scholarship holder from 1957, docent from 1960 and professor from 1966 to 1991. He then retired to a position as professor emeritus.