Arsenal signed Forbes in March 1948 for a fee of £15,000. The move was encouraged by Forbes' Scotland teammate Archie Macaulay, who subsequently lost his place in the Arsenal team to Forbes. Arsenal won the English league championship in 1947–48 and the FA Cup in 1950. Forbes played an important role in the latter victory, as Arsenal defeated Liverpool 2–0 in the final. Arsenal reached another FA Cup final in 1952, but they lost 1–0 to Newcastle. The club then won another league championship in 1952–53, finishing ahead of Preston on goal average.