The former world number one trailed 3-5 in the first set to Barrois, who was contesting her first ever WTA final, but hit back to take it 7-5 and then cruised to victory in the second set.
Sharapova had already beaten three-time Strasbourg champion and clay specialist Anabel Medina Garrigues of Spain in Friday's semi-final.
The 23-year-old Russian superstar, who also tasted success at Memphis in February, has been seeded 12th for the French Open beginning on Sunday.
Victory at Strasbourg represents her 22nd career title, which includes three Grand Slams, and her first on red clay, after a green clay win at Amelia Island in 2008.
Sharapova returned to competition in the middle of last year after a long spell on the sidelines due to a shoulder injury and is currently ranked 13th in the world.
She is not among the favourites at Roland Garros, where she reached the semi-finals in 2007 and the quarter-finals last year.