He was drafted by the Vikings in the 13th round of the 1965 NFL Draft with the 176th overall pick. His first contract was worth $9,000.00. In his rookie year of 1965, Osborn had 20 carries for 106 yards for two touchdowns, while also having one reception for four yards. He returned 18 kickoff returns for 422 yards. The next year, his carries increased significantly as he carried the ball 87 times for 344 yards and one touchdown, while having 15 receptions for 141 yards and 2 touchdowns. He also returned one kickoff return for 19 yards. His third year in 1967 was his peak as he carried the ball 215 times for 972 yards while having 2 touchdowns and 34 receptions for 272 yards. He played just four games in the 1968 season, while having 42 carries for 140 yards. His team participated in the playoffs that season; in the Western Conference Championship, he had 5 carries for 4 yards while having one catch for -2 yards as his team lost 24-14 to the Baltimore Colts. He returned to play in each game of the 1969 season, while having 186 carries for 643 yards and 7 touchdowns. He had 22 receptions for 236 yards and one touchdown. That year, his team went on a playoff run, and he played in each of the three game that year. In the Divisional Round game versus the Los Angeles Rams, he had two touchdowns, one being in the first quarter that evened the score and the other in the third quarter that narrowed the deficit to 17-14. He finished with 13 carries for 30 yards in the 23-20 Viking win. In the 1969 NFL Championship Game, he had a 20-yard touchdown run in the third quarter that made it 24-0, with the final score being 27-7 over the Cleveland Browns. He finished with 18 carries for 108 yards. In Super Bowl IV, he was the starting halfback in the game versus the Kansas City Chiefs. In the third quarter, he scored a touchdown from four yards out to narrow the deficit to 16-7, with the final score being a 23-7 loss. He had 7 carries for 15 yards while having 2 receptions for 11 yards. The following year, he played in all 14 games while starting in 10 of them while having 207 carries for 681 yards and five touchdowns. He also had 23 catches for 202 yards and one touchdown. He was named to the Pro Bowl that year, the lone selection of his career. In his team's playoff appearance that year, he had 12 carries for 41 yards in the team's 17-14 loss to the San Francisco 49ers. In 1971, he played in 11 games, carrying the ball 123 times for 349 yards and five touchdowns along with 25 receptions for 195 yards and one touchdown. In his team's playoff appearance that year, he had six carries of 13 yards in the 20-12 loss to the Dallas Cowboys. He played in every game of the 1972 season, carrying the ball 82 times for 261 yards for two touchdowns and having 20 receptions for 166 yards. In the following year, he played in 11 games, carrying th ball 48 times for 216 yards while having three catches for four yards. It was his first season with no touchdowns since 1968. In the team's playoff run that year, he played minimally, having 4 carries for 27 yards. The 1974 season, he played in 13 games, rushing 131 times for 514 yards and four touchdowns while catching the ball 29 times for 196 yards and having 1 kick return for 14 yards. In his team's playoff run that year, he played in each game as his team advanced to the Super Bowl once again. In the Division Round vs the St. Louis Cardinals, he had 16 carries for 67 yards while having 4 receptions for 36 yards as his team won 30-14. In the NFC Championship vs the Los Angeles Rams, he scored on a one yard touchdown run to make the score 14-3 as his team held on to win 14-10. He had 20 carries for 76 yards while having a reception for one yard. In Super Bowl IX versus the Pittsburgh Steelers, he had 8 carries for -1 yards while having 2 catches for 7 yards in a 16-6 loss. The 1975 season was his last with the Vikings; he carried the ball 32 times for 94 yards and one touchdown while having one reception for -4 yards along with 1 kick return for 38 yards. He did not have any carries in the Vikings' playoff run that year, but he had one kick return for no yards as his team lost 17-14 to the Cowboys. In 1976, he joined the Green Bay Packers. He played in six games while having six carries for 16 yards while having three kick returns for 19 yards. Osborn finished in the top 10 in rushing attempts in the league three times, doing so in 1967, 1969, and 1970.
