Philippe Baby Casgrain (December 30, 1826 – May 23, 1917) was a Quebec lawyer, author and political figure.

He represented L'Islet in the House of Commons of Canada as a Liberal member from 1873 to 1891.

He was born in Quebec City in 1826, the son of Charles-Eusèbe Casgrain, and studied at the College of Ste.

He articled in law with Jean-Thomas Taschereau, was called to the bar in 1850 and practiced at Quebec with Pierre Joseph Olivier Chauveau.

Casgrain published a number of works on the history of Canada, including: He died at Quebec in 1917.