Cornwell made his first grade debut for Western Suburbs in Round 4 of the 1930 season against St George.
That same year, Cornwell was a member of the Western Suburbs side which claimed their first ever premiership defeating St George 27–2 in the grand final challenge.
Wests had lost the original grand final but as minor premiers were allowed to challenge the winner for a rematch.
The following year in 1932, Wests suffered a similar fate losing to Souths again in the 1932 grand final challenge 9–2.
In 1933, Cornwell and Wests endured a poor season finishing last on the table but the following year in 1934 they went from wooden spooners to premiers defeating Eastern Suburbs 15–12 in the grand final, a feat that no team as of 2018 has matched since.