Parkin passed a two-year apprenticeship to win a professional contract at Blackburn Rovers to earn a contract under manager Jim Smith in March 1976. He made his competitive debut at Bristol Rovers on 8 March 1976. Rovers finished 12th in the Second Division in 1976–77, before rising up to fifth place in 1977–78. The club suffered relegation under new boss John Pickering in 1978–79, before Howard Kendall took charge in his first job in management. In his three years at Ewood Park, Parkin made 13 league appearances, all but one of which were as a stand-in for the injured Glenn Keeley towards the end of the 1978–79 season.
Parkin left Malmö Stadion and returned to England in August 1981 with Bristol Rovers, though had to spend a day as an Almondsbury Greenway player to get around rules governing Swedish transfers. The "Pirates" finished 15th in the Third Division in 1981–82 under the stewardship of manager Bobby Gould. The "Gas" rose to seventh in 1982–83, before David Williams was put in charge. He led the club to fifth and sixth places finishes in 1983–84 and 1984–85. Bobby Gould was then re-appointed as manager, but could only lead Rovers to a 16th-place finish in 1985–86. In five years at Eastville Stadium, Parkin played 206 league games and was named as the club's Player of the Year for 1985 and 1986.
Swindon Town
He transferred to Swindon Town for a £27,500 fee in July 1986. He formed a consistent centre-back partnership with Colin Calderwood, and played 48 games in 1986–87. The "Robins" won promotion out of the Third Division after beating Gillingham 2–0 at Selhurst Park in the play-off Final. He was voted Player of the Season after he scored four goals in 54 games in 1987–88, as Lou Macari's side secured a comfortable mid-table position. He featured 36 times in 1988–89, as Swindon reached the play-offs, where they were beaten by Crystal Palace. Osvaldo Ardiles then took charge at County Ground, who preferred to play Jon Gittens instead of Parkin.
Port Vale
He was signed by Port Vale for £60,000 in December 1989. Manager John Rudge used him only 12 times in the Second Division in 1989–90. He became a regular in the first team from October 1990, and played 32 times in 1990–91. However he lost his place in August 1991 and was loaned out to Shrewsbury Town the next month, featuring in five Third Division games for John Bond's "Shrews" at the Gay Meadow. He returned to Vale Park the next month only to be handed a free transfer in May 1992, having played just eight games for the "Valiants" in the 1991–92 relegation campaign.
Darlington
He moved onto Darlington, where he was made player-coach. The "Quakers" finished 15th in the Third Division in 1992–93. Parkin took caretaker control of the team in October 1993 when Billy McEwan was dismissed; Forrest and Parkin took charge of the first-team for four matches before Alan Murray took over permanently. Murray could only take the club to one place above the bottom of the English Football League in 1993–94. Parkin departed Feethams and moved on to Barrow of the Northern Premier League in November 1993, where he was made player-assistant manager, before retiring as a player following a broken leg.
