Woosnam was born in the town of Oswestry, Shropshire in England, and his family lived in the nearby village of St Martin’s in Shropshire. He started playing at the unique Llanymynech Golf Club, which straddles the Wales-England border. He played as an amateur in regional competitions in the English county of Shropshire alongside Sandy Lyle.

Woosnam turned professional in 1976 and first played the European Tour in 1979. After three modest seasons his career took off in 1982 when he won the Swiss Open and came eighth on the Order of Merit (prize money list). He also finished in the top ten on the Order of Merit every year from 1983 to 1991 and again in 1993, 1996, and 1997, making thirteen times in all. In 1987 and 1990 he was first, and in the former year he set a world record for global tournament earnings of £1,062,662.

Woosnam placed third in the 1986 Open Championship. In 1991, he reached the top of the Official World Golf Rankings, eventually spending a total of 50 weeks as World Number 1. In the same year, he emulated his British rivals, Sandy Lyle and Nick Faldo, by winning the Masters Tournament; the first person representing Wales to ever win a major championship. He has won 28 official money events on the European Tour and many other events around the world.

Woosnam was awarded an O.B.E. in the 2007 New Years Honours List. He now lives in Jersey.

On 1 June 2008, Woosnam won his first stroke play title in 11 years at the Parkridge Polish Seniors Championship at Krakow Valley Golf and Country Club, finishing with a course record 63. The tournament was his third appearance on European Seniors Tour, which he joined after turning 50 years old in March 2008.