Goals from Benjamin Corgnet and Romain Hamouma had put Les Verts 2-0 up at the Stade Geoffroy-Guichard, but the game turned when Fabian Lemoine received a second yellow in the 59th minute for a foul on Ezequiel Lavezzi.
"There's disappointment when leading by two goals and again in stoppage time," Galtier told reporters. "I am proud of what the players have done. The exclusion of Fabien Lemoine was the turning point. The red card is harsh. This automatically creates frustration.
"We knew it would be difficult even leading by two goals. If someone had told me before the game that we would share the points against Paris, I would have said that this is a favorable result.
"It was an interesting game for everyone. I remember the positives."
Saint-Etienne are seventh in Ligue 1.