Porter, who played 27 games with the Longhorns, has two years of eligibility remaining and will be eligible this season after he graduates from Texas this summer.
The Katy (Texas) High School product was the No. 229 recruit in the 2016 ESPN 300 and saw regular playing time in his first two seasons in Austin, logging a combined 129 carries for 467 yards and four touchdowns.
In 2018, Porter appeared in the first four games of the Longhorns season but tallied only one carry. He entered the transfer portal following the season. He'll join a Cougars team that welcomed a new coach in January, former West Virginia coach Dana Holgorsen.
The Cougars, who started spring drills on March 19, wrap up with their annual spring game on April 12.