Mitchell persuaded Dewar to join Blackburn (along with Tom Brandon and Harry Campbell);[1] in doing so, he brought an end to his international career as at this time Scotland did not select men playing in England.

In the FA Cup final against Sheffield Wednesday (from the Football Alliance) at The Oval on 29 March 1890, Rovers were the odds-on favourites to win in view both of their record of three victories in the previous six seasons and their superior league placing.

Rovers lived up to expectations as they romped away with the Cup defeating their Yorkshire opponents 6–1 with goals by Billy Townley (3), Nat Walton, Jack Southworth and Joe Lofthouse.

In the final, played at Kennington Oval on 21 March, Rovers put County under pressure from the beginning and in the 8th minute, centre-half Dewar scored from a Townley corner.

Jimmy Oswald of Notts County scored a late consolation goal but Blackburn finished comfortable 3–1 winners and won the FA Cup for the fifth time in eight years.