Under manager John Neal he helped Wrexham establish their giant-killing reputation by reaching the quarter finals of the FA Cup in 1974 and the quarter finals of the European Cup Winners' Cup in 1976, when they lost to the eventual winners, Anderlecht of Belgium. After helping Wrexham storm to the Third Division title in 1977–78, Thomas crossed the border to England and joined Manchester United. He played 110 games and scored 15 goals for the Red Devils, collecting an FA Cup runners-up medal in 1979.
Under manager John Neal, Thomas assisted Wrexham in establishing their reputation for defeating strong opponents by reaching the quarter finals of the FA Cup in 1974 and the European Cup Winners' Cup in 1976, when they lost to eventual winners Anderlecht from Belgium. After leading Wrexham to win Third Division title in 1977–78, Thomas crossed into England and joined Manchester United. He played 110 games and scored 15 goals for the Red Devils, winning an FA Cup runners-up medal in 1979.