"Life's journey has unexpected peaks and valleys. I am thankful for every step I've been able to take," Hilinski wrote in a statement he posted on Twitter. "I am grateful for my amazing family and all of those that have helped me along the way as I chase my dreams. I'm excited to being this next chapter at Northwestern University."
After starting the Gamecocks' final 11 games as a freshman in 2019, throwing for 2,357 yards with 11 touchdowns and five interceptions, Hilinski appeared in just two games in 2020 with six pass attempts.
A native of Southern California, Hilinski was the No. 4-ranked pocket passer in the Class of 2019.
His family created the Hilinski's Hope Foundation to support mental health for student athletes, after his older brother, Tyler, then a quarterback at Washington State, died by suicide in January 2018.
Northwestern is looking to replace outgoing senior Peyton Ramsey, who threw for 1,733 with 12 touchdowns and eight interceptions in nine games in 2020. Ramsey has accepted an invitation to play in the Hula Bowl on Jan. 31.