Westgarth was a successful football coach after a playing career achieved little of note. He was South Shields' assistant trainer before he joined Ebbw Vale, Workington and Luton Town in a training capacity. In 1938 he joined Stockport County as trainer-manager.
He had a successful spell at Hartlepools during the mid-1950s. In 1955 the club reached the 4th round of the FA Cup, its best ever performance. In 1956-57 Hartlepools narrowly missed out on winning Division Three (North). But in 1957 he was taken seriously ill and died on February 4 shortly after he saw his side lose 4-3 to Manchester United in the FA Cup Third Round in front of a record 17,264 crowd at Victoria Park.