McCombs became a successful businessman, owning and operating a drapery in Christchurch. He became a trade unionist and was elected president of the Drapers' Assistants Union. Regarded as a moderate among the union movement, he was regarded by liberal newspapers as representing "sane labour". McCombs also spent time speculating in property. In several areas in and around Christchurch he bought and sold land, the transactions that were not always profitable however and gradually the grounds of his family home in Fendalton were subdivided and sold to repay debts.