The right-hander underwent flexor tendon repair surgery Tuesday, according to a team announcement. During the procedure, it was also determined he would require Tommy John surgery.
Taillon will be out of action until 2021, according to MLB.com's Adam Berry.
Taillon hasn't pitched since May with what was first diagnosed as a right elbow flexor strain.
He was shut down and sent to see a doctor on July 24 after feeling renewed pain in his right elbow when he began to throw from 90 feet away.
It's a tough break for the former first-round draft choice, who also underwent Tommy John in 2014.
After a strong 2018 campaign where he tossed 191 innings that included two complete games and a 3.20 ERA, Taillon made seven starts this season for Pittsburgh, authoring a 4.10 ERA and 1.13 WHIP in 37 1/3 innings.