Ehlinger graduated as the school's all-time leader in passing yards and touchdowns, surpassing Super Bowl-winning quarterbacks Drew Brees and Nick Foles.

[2] Sources: Ehlinger joined the Texas Longhorns under new head coach Tom Herman, who inherited an offense led by sophomore starting quarterback Shane Buechele.

[5] During the spring game on April 15, Ehlinger played on the second-team offense against the first-team defense, scoring a touchdown and passing for 148 yards.

[11] Ehlinger was able to connect with wide receiver Armanti Foreman on a 17-yard touchdown pass with 45 seconds remaining in regulation to give the Longhorns a late lead before the Trojans equalized with a field goal to send the game into overtime.

[14] However, given the severity of Buechele's injury, Ehlinger started at quarterback for the Longhorns against the Kansas State Wildcats, leading Texas to a 40–34 double overtime victory.

[11] During the fourth quarter of the game, Ehlinger briefly laid motionless following a hard tackle, sitting out a subsequent play to undergo concussion protocol before later returning to the field.

Although Ehlinger stated in the post-game press conference that he "felt fine" and "wasn't ever confused where [he] was at all," Boston University Center for the Study of Traumatic Encephalopathy co-founder Christopher Nowinski expressed skepticism on Twitter that concussion protocol was properly followed.

[22] He was cleared to play against the Kansas Jayhawks the following week,[23] serving as a backup quarterback and completing two passes and scoring one touchdown in the fourth quarter in the Longhorns' victory.

[24] He did not start at quarterback against the 24th-ranked West Virginia Mountaineers but assumed the role after two offensive series, throwing for two touchdowns as well as recording a 23-yard catch from Jerrod Heard in the 28–14 win.

[26] Although he played well for much of the game in maintaining a lead for the Longhorns, Ehlinger threw an interception that was returned 55 yards in the closing minutes of the fourth quarter, eventually setting up a go-ahead touchdown from Texas Tech.

Ehlinger threw a second interception on Texas' final offensive opportunity to reclaim the lead, resulting in a 27–23 loss to end the regular season.

[28] Buechele would eventually be prioritized for the bowl game, with Herman and Beck citing concerns over Ehlinger's protection of the football as a deciding factor.

[11][30] With the win, Ehlinger finished the season with a 2–4 record as a starter with playing time in nine total games;[11] he was also the team's leading passer and rusher by yardage.

Both Ehlinger and Buechele remained the primary candidates for the position, alongside newly recruited quarterbacks Cameron Rising and Casey Thompson.

[36] On August 20, coach Herman announced that Ehlinger would be the starting quarterback for the season opener against the Maryland Terrapins, lauding his improvements in throwing the football and his pocket presence.

Ehlinger completed 21 of 39 passes for 263 yards and 2 touchdowns but threw two costly interceptions late in the fourth quarter, ensuring a Terrapins victory.

[39] Coach Herman expressed continued confidence in Ehlinger in the starting role despite the disappointing performance to close out the loss to Maryland, iterating that he did not doubt the quarterback's skills.

[53] A break in play afforded by a bye gave Ehlinger more time to recover, allowing him to start at quarterback against Oklahoma State on October 27.

[54][55] In Stillwater, Oklahoma, Ehlinger scored four total touchdowns and threw for 283 yards, narrowing a 17-point halftime deficit that ended in a 38–35 loss.

[61][46] However, he was cleared shortly after to play in the final regular season game against the Kansas Jayhawks where he threw for two touchdowns and ran for another in a 24–17 victory.

[46] In the post-game press conference, Ehlinger asserted that he "would make it my mission to never let [the Longhorns] or [the University of Texas] feel this disappointment again," a sentiment that drew comparisons to a famous speech given by Tim Tebow following a loss to Ole Miss in 2008.

On the heels of a strong sophomore campaign, Ehlinger was named one of the early favorites to win the 2019 Heisman Trophy in December 2018 and was a preseason candidate for the Walter Camp Player of the Year and Manning Award.

[71] The Dallas Morning News considered him the best quarterback in the Big 12 Conference entering the season and he made numerous Preseason All-Big 12 and All-American lists.

[85] In his first start against the Washington Commanders, Ehlinger completed 17 of 23 pass attempts for 201 yards, but also lost a fumble in the red zone in a 17–16 home loss.

[86] After a 26–3 loss to the New England Patriots, where Ehlinger threw for just 103 yards and an interception, head coach Frank Reich was fired, and interim Jeff Saturday announced that Ryan would return to the starting role against the Las Vegas Raiders.