Born in Belfast, Nelson attended the Royal Belfast Academical Institution a school better known for its Rugby feats. On his 17th birthday in 1966, Nelson joined Arsenal. Originally a left-winger, he later moved back into defence to become a left back. An aggressive, hard-tackling player, Nelson was a crowd favourite and known for his cheeky sense of humour. Nelson played in the FA Youth Cup of Final of 1966 which the Gooners won in two legs over Sunderland
He was a regular in Arsenal's reserve side for several seasons, before making his first-team debut against Ipswich Town on 25 October 1969. He was understudy to the Gunners' established left wing, Bob McNab, and it wasn't until McNab was injured in the 1971–72 season did Nelson become a regular. Even then, whenever McNab returned from injury, Nelson was forced to step down to being reserve. He only played four league matches during Arsenal's 1970-71 Double-winning campaign, which was not sufficient to win a medal.
McNab left Arsenal in the summer of 1975, and Nelson finally became Arsenal's first-choice left back. For the next five seasons he was a near ever-present in the Arsenal side, and he played in all three of the Gunners' successive FA Cup finals of 1978, 1979 and, in 1980. Nelson started the middle of the three, wherein Manchester United were beaten at Wembley by a 3-2 scoreline. As well as in Arsenal's Cup Winners' Cup Final of 1980 to Valencia which was lost on penalties.
With the arrival of England international Kenny Sansom at the club in 1980, Nelson once again found himself out of the first team and thus left Arsenal in 1981. He played 339 first-class matches for the Gunners in total, and scored 12 goals.
Shortly thereafter Sammy joined Brighton & Hove Albion. Nelson spent two seasons at Brighton; although unable to save the side from relegation in 1982–83, they did reach another Cup final that season, losing to Manchester United 4–0 in a replay, after a 2–2 draw in the final, but Nelson missed the game. He retired as a footballer that summer, and after spending a season as a coach at Brighton, he left the game completely and is currently a tour guide at Arsenal's Emirates Stadium as part of their "Legends Tour".
In the meantime, Nelson had made his debut for Northern Ireland, as a sub against England on 21 April 1970. Nelson went on to win 51 international caps, two of which came in Northern Ireland's matches of the 1982 FIFA World Cup.
After retirement, he went into the insurance industry. Nelson is married to wife Helen and they have a daughter named Emily and their two sons Peter and James. Emily is married to English cricketer Matt Prior, of whom have a son by the name of Jonathan.Arsenal
FA Youth Cup - 1966
FA Cup - 1979