USDAW became the fourth union to back Mr Leonard, the favoured candidate of the left, following TSSA, ASLEF and Unite. In the past USDAW has given its backing to a moderate Labour candidate in previous leadership elections. In 2014 it backed Jim Murphy in his battle with left-winger Neil Findlay for the leadership.
In the current battle with Anas Sarwar, Mr Leonard is the only one of the two candidates to receive any union endorsements so far.
Mr Leonard said: “I’m delighted to win the support of USDAW, a union I have worked closely with to promote workers’ rights in Scotland’s retail, distribution and manufacturing industries for twenty five years.”
A spokesperson for Mr Leonard’s campaign said: “This is a fantastic endorsement for Richard’s ideas. USDAW have always been seen as being on the right wing of the Labour Party. Their support shows that Richard’s message of real change is gaining support across the whole spectrum of Labour Party opinion, and that he is the candidate who can unite the party effectively.”