Philip Nicholas Seton Mansergh, OBE (27 June 1910 – 16 January 1991) was a historian of Ireland and the British Commonwealth.
As the Smuts Professor of Commonwealth History at Cambridge University after 1953, he trained many of the specialists in the field of Irish, Indian, and Commonwealth studies.
He played the central role in assembling and editing the "monumental" 12-volume edition of historical documents associated with the independence of India.