[1] Upon leaving the Bills, Losman signed with the Las Vegas Locomotives in the upstart United Football League, leading the team to winning the inaugural UFL championship game before finishing out his career with stints with the Oakland Raiders, Seattle Seahawks, and Miami Dolphins.

3 quarterback in the nation by PrepStar magazine, Losman accepted an athletic scholarship to attend college at University of California, Los Angeles (UCLA).

Losman eventually transferred to Tulane University in New Orleans to play for then-head coach Chris Scelfo, who had made a late recruiting run at him just prior to his committing to UCLA.

Like Kelly, Losman was drafted in a quarterback-rich class, and was the fourth (and final) quarterback taken in the first round that year, following Eli Manning, Philip Rivers, and Ben Roethlisberger.

[6] He eventually recovered and saw limited action in the 2004 NFL season, appearing briefly in three games and completing 3-of-5 passes for 32 yards and 1 interception while backing up Drew Bledsoe.

Following the Bills' February 2005 release of Bledsoe, Losman was named the team's starting quarterback by head coach Mike Mularkey.

Following the season, the Bills further bolstered their offensive line in free agency, signing guard Derrick Dockery, right tackle Langston Walker, and guard/center Jason Whittle.

[9] Edwards was considered by many to be the 3rd best available quarterback prospect in the draft (behind #1 overall JaMarcus Russell and #22 overall Brady Quinn), but waited until late in the 3rd round prior to the Bills selection.

[citation needed] On September 23, Losman suffered a grade one sprain of his left knee in the first series of plays in a game against New England.

[10] Losman was hit late after completing a four-yard pass to Marshawn Lynch by New England Patriots nose tackle Vince Wilfork, who was assessed a 15-yard roughing the passer penalty.

The reports continued to allege that team owner Ralph Wilson, Jr. wanted Losman benched so that he could not reach the statistical milestones needed for his bonus.

Losman led the Bills on two consecutive scoring drives, including one that ended with an 85-yard touchdown pass to wide receiver Lee Evans.

[15] Though he wanted to be traded,[15] Losman continued playing for the Bills in 2008, filling in for an injured Trent Edwards intermittently throughout the season with limited success.

Looking back at Losman's stint with Buffalo, former Bills vice president of player personnel John Guy was quoted as saying "J.P. never had a fair chance.

[19] Losman made his first Oakland, California appearance against the Denver Broncos on December 20, 2009, throwing one incomplete pass after both quarterbacks Charlie Frye and JaMarcus Russell suffered injuries and had to leave the game.

[22][23] Following his NFL career, Losman became a volunteer coach with the New Canaan High School football team after settling with his family in the Connecticut suburbs of New York City.

[24] He eventually became an offensive coach, and in March 2019, while taking part in throwing drills at Clemson's Pro Day, was asked by an NFL scout if he would consider returning to the league despite not having played since 2011; Losman declined.