Oosterhuis represented Great Britain in the 1967 Walker Cup and in the 1968 Eisenhower Trophy. He played on the European Tour in the early years of his professional career, and won four consecutive Order of Merit titles from 1971 to 1974. He was also the leading money winner in 1972 and 1974 (the two did not necessarily coincide at that time, because the Order of Merit was based on a points system). He then moved to the U.S.-based PGA Tour, which he played full time from 1975 until 1986. He collected 20 victories worldwide including the 1981 British PGA Championship. He was the runner-up in The Open Championship in 1974 and 1982.
Oosterhuis played on six Ryder Cup teams for Great Britain or Europe from 1971 to 1981. His notable Ryder Cup singles victories include wins over Arnold Palmer and Johnny Miller.
From 1987 to 1993, he was Director of Golf at Forsgate Country Club in Jamesburg, New Jersey, and at the Riviera Country Club in Pacific Palisades, California.
In 1994, Oosterhuis was hired to cover the PGA Tour by Britain's Sky Sports and covered two Open Championships for the BBC. From 1995 to 1997, he was the lead analyst for the Golf Channel's coverage of the European Tour.
In 1998, Oosterhuis joined the CBS Sports golf announcer team full time. In addition to his CBS analyst duties, he also serves as a contributing analyst for the Golf Channel's Pre and Post-Game Show.