| Philippe Baby Casgrain | |
| Constituency Mp: | L'Islet |
| Parliament: | Canadian |
| Predecessor: | Barthélemy Pouliot |
| Successor: | Louis-Georges Desjardins |
| Term Start: | 1872 |
| Term End: | 1891 |
| Birth Date: | 30 December 1826 |
| Birth Place: | Quebec City, Lower Canada |
| Party: | Liberal |
| Relations: | Charles-Eusèbe Casgrain, father Thomas Chase-Casgrain, nephew Louis Beaubien, cousin Luc Letellier de St-Just, cousin |
| Children: | Joseph Philippe Baby Casgrain |
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. Anne de la Pocatière. He articled in law with Jean-Thomas Taschereau, was called to the bar in 1850 and practiced at Quebec with Pierre Joseph Olivier Chauveau. In 1854, he married Mathilde Perrault. He was named deputy prothonotary for the Quebec Superior Court in Quebec district. Casgrain was named Queen's Counsel in 1879. After he retired from politics, he was clerk for the Quebec Circuit and Revision Court. He served several terms as president of the Literary and Historical Society of Quebec.
Casgrain published a number of works on the history of Canada, including:
He died at Quebec in 1917.
His son Joseph Philippe Baby became a member of the Canadian Senate.