Ambrose comes onto the senior list in place of midfielder Alex Browne, who will miss the entire season after having a knee reconstruction.
Ambrose, an athletic 185cm forward, was taken by the Bombers with pick No.26 in the 2014 NAB AFL Rookie Draft.
He played with Essendon's AFL team last season after being recruited from Old Xaverians in the VAFA competition.
"We could not have been more pleased with the way Patrick has applied himself at training since we drafted him in the rookie draft," Essendon's acting general manager of football, Steve Alessio, told the club website.
"He is a great athlete with both endurance and strength and we think his elevation to the senior list is a great reward for all of his hard work."
Ambrose has been seen by many at Essendon as a like-for-like replacement for Stewart Crameri, who was traded to the Western Bulldogs in the off-season.
