In 1981, Kemp signed with
the Los Angeles Rams as an undrafted free agent. Kemp was one of four quarterbacks the Rams carried on the roster that season. When former starter
Vince Ferragamo bolted the Rams to sign with Montreal of the
Canadian Football League, the Rams inserted
Pat Haden as the full time starter, with Raiders cast off
Dan Pastorini as the second string and former draft pick
Jeff Rutledge as the third stringer quarterback. Pastorini drew the start against
the Washington Redskins and was ineffective, going 8 for 21 and two interceptions. With the Rams down 30–7, Kemp made his NFL debut late in the game. He went two for six with an interception. Kemp would not see the field at all during the strike shortened 1982 season and made a handful of appearances during the 1983 season. One of those was a token appearance to do a kneel down during the Rams 41–17 blow out win against
the Buffalo Bills, a team his father starred for and won a championship with in the American Football League during the 1960s. That season the Rams made the playoffs and faced the Redskins in the Divisional playoff game. Ferragamo played one of the worst games of his career, throwing three interceptions. He was benched in favor of Kemp later in the eventual 51–7 loss. In 1984, after Ferragamo went 1–3 as a starter to begin the season, head coach
John Robinson made the switch, benching the one-time Rams star in favor of Kemp. Kemp started the rest of the season, and finished with a 9–4 record as a starter, completing 143 passes out of 284 attempts for 2,021 yards, with thirteen touchdown passes against seven interceptions. The Rams finished 10–6 but lost to
the New York Giants in the Wild Card Round. The following season, the Rams traded Ferragamo to
the Buffalo Bills for tight end Tony Hunter. Despite Ferragamo being gone, Kemp was not assured to be the starter. Despite the poise and ability to start he showed during the 1984 season, the Rams signed Canadian League star
Dieter Brock to be the team's starting quarterback. Kemp only made one start that season, a 24–17 loss to the Giants. The Rams cast their luck with Brock, who did manage to lead the team to the playoffs, where they were trounced by
the Chicago Bears and their vaunted 4–6 defense in the NFC Championship. The following season, the Rams revamped their quarterback rotation again as Brock suffered an injury during preseason that later led to him retiring, while the Rams signed former
Falcon star
Steve Bartkowski and acquired
Jim Everett from
the Houston Oilers. Kemp was not re-signed and played the 1986 season with the Rams rival
San Francisco 49ers, where he backed-up
Joe Montana. When Montana was injured, Kemp started six games, going 3–2–1 during that period. One of those games was a 31–16 win over
the Miami Dolphins, coached by
Don Shula, father of
Dave Shula, one of Kemp's teammates at Dartmouth. The next season, Kemp was with
the Seattle Seahawks and was one of the players who crossed the picket lines. He won his only start that year, a 32–17 victory over a
Detroit Lions team made up of mainly replacement players. Kemp would play with the Seahawks for the bulk of his remaining years in the NFL. He was released during the 1991 season, but quickly found a job with
the Philadelphia Eagles. The Eagles struggled at quarterback that season, mainly with injuries. Starter
Randall Cunningham went down, followed by backup
Jim McMahon. Rookie
Brad Goebel was inserted, but quickly too was a victim of the injury bug. The Eagles signed Kemp, and then coaxed former
New York Jets quarterback
Pat Ryan out of retirement. Kemp started two games for the Eagles, going one and one. The 1991 season was Kemp's last as an NFL player. He finished with a 16–12–1 record as a starter, and 39 touchdowns versus 40 interceptions. ==Post NFL career==