He was born in Scotland around 1740 and came to Quebec around 1760. McBeath entered the fur trade in 1765, travelling to the Lake Superior region. In 1772, he became part of a company based at Michilimackinac. He became partners with Simon McTavish and then went into business on his own. With Peter Pond and others, McBeath purchased shares in the North West Company, which he held until 1787. He settled at L'Assomption in 1785.
He was named justice of the peace for Montreal district in 1795 and, in 1799, he was appointed customs collector for the port of St Johns (later Saint-Jean-sur-Richelieu). McBeath also served as lieutenant-colonel in the militia and was reportedly a Freemason.
He died at Montreal in 1812.