He also established the Big Ten Conference career passing efficiency record that would stand for six seasons until it was surpassed by Joe Germaine. He was a two-time national passing efficiency champion during his junior and senior seasons. He was a three-time Big Ten champion in this statistic.
Grbac was drafted in the eighth round of the 1993 NFL Draft by the 49ers. He served as Steve Young's backup from 1994 to 1996. In 1997, Grbac signed with the Kansas City Chiefs to be their starting quarterback. During the 1997 season, the Chiefs finished first in the NFL with a 13–3 record but lost a divisional playoff game against the Denver Broncos. Grbac's best season statistically came in 2000 when he passed for 4,169 yards and 28 touchdowns with a passer rating of 89.9 en route to the Pro Bowl.
Grbac also played for the Baltimore Ravens before retiring after the 2001 season when the Ravens cut him in a salary cap move after he refused to renegotiate his contract. At the time of his retirement, Grbac had been in negotiations with the Denver Broncos—Denver was interested in signing him as a backup to starting quarterback Brian Griese, but Grbac opted for retirement.
The Baltimore Ravens were defending Super Bowl champions when Grbac replaced quarterback Trent Dilfer at the start of the 2001 season. Upon signing, Grbac mocked Dilfer in the press: "It's time that a quarterback comes in here and provides leadership, a go-to guy, a vertical passing game. This is a great team. I can make it better." Grbac posted mediocre passing statistics that year, but still managed to lead the Ravens to an 10-6 regular season record and a playoff win over the Miami Dolphins before losing in the second round to the Pittsburgh Steelers. During the season, he was taunted and booed by Baltimore fans and harshly criticized by the Baltimore press. When Grbac was injured midway through the season and temporarily replaced by backup Randall Cunningham, the taunt "Elvis has left the building" was used. Grbac was jeered upon his return to the lineup after Cunningham went 2–0 as a starter.
Grbac was featured as People's Sexiest Athlete in 1998. Sportswriter Jeff Pearlman claims this was because of a mistake by a photographer, told to photograph "the Chiefs quarterback," who accidentally photographed Grbac instead of the intended Rich Gannon.