He returned to Branch where, playing in socks, as his feet had grown to size 17, he scored 68 points and had 38 rebounds against Vanndale.

However, Barnes was ruled ineligible after one season, after recruiting allegations surfaced and the team had to forfeit 22 games.

Barnes chose Cameron after being recruited by Coach Henry Iba and Oklahoma A & M (now Oklahoma State) in Stillwater, saying later, “I just didn’t think academically I had the foundation to make it at a big college.”[6] He tallied 28.8 points per game in his freshman year (1960–1961) and 30.6 points per game in his sophomore year.

[2][6] In 1962–63 Barnes averaged a double-double of 18.9 points and 16.5 rebounds, shooting 50.3% from the field and 76.2% from the line, for the Texas Western Miners.

[9][10] The 1963–64 Miners finished 25–3 and advanced to the 1964 NCAA University Division basketball tournament, where they were defeated by Kansas State in the Midwest Regional Semi-Final as Barnes fouled out of the game.

[12] Barnes won an NBA Championship with the Celtics in 1968–1969, serving at the backup to Bill Russell, although hampered by injury, he did not appear in the playoffs.

Barnes' career then ended in 1971 after 11 games with Baltimore and brief stints with the Binghamton Flyers / Trenton Pat Pavers of the Eastern Basketball Association.

The USA team, coached by Henry Iba won the gold medal in the Tokyo Games when they defeated USSR, 73–59.

[2] Of his Olympic experience, Barnes recalled, "Mr. Iba didn't want me practicing with the team because he was afraid I might hurt someone, I was kind of rough and tough.

"[5] Barnes was the top field-goal shooter (53 percent) on the Olympic squad, averaging 8.5 points in the teams' nine games.

Barnes roomed with Bill Bradley and had Walt Hazzard and Larry Brown among his teammates[5] Celtics' coach and general manager, Red Auerbach, said of Barnes: "Jim's many friends and associates affectionately called him 'Bad News' [for the damage he did to opposing teams and players], but he was always 'Good News' to me.

"[14] College teammate at UTEP Steve Tendennick said of Barnes, "He had a fantastic disposition,he was a gentle guy, but competitive.

Barnes was a board member of the Washington D.C. organization "Kids in Trouble Inc." There, Barnes was involved in an annual celebrity tennis event, provided school counseling, was active in events on stopping youth violence and was a volunteer basketball coach for a local church team.

Barnes advised star Maryland football player LaMont Jordan to focus on his studies and stay in school as an underclassman.