Record label BMG (search) said Stewart, 60, went down on one knee and proposed to 33-year-old Penny Lancaster at the French landmark on Wednesday. She accepted.
"I left it this long because I wanted to get it right this time," Stewart said in a statement. "I've never been happier and more in love than I am today."
BMG said the couple, who have dated for more than five years, plan to marry later this year.
Lancaster's agent, Nicholas Young, said the couple would make wedding plans once Stewart's divorce from model Rachel Hunter is finalized. "Rod's preference is to get married in Scotland," Young said.
The raspy-voiced rock star was previously married to Alana Stewart.