The bookmakers have both named the former London mayor as even money favourite to become the next elected Conservative leader, with William Hill cutting Johnson from 11/4, and Ladbrokes cutting his price from 6/4.
Home secretary Theresa may is the 7/2 second favourite at William Hill, or 3/1 at Ladbrokes, followed by Michael Gove and Andrea Leadsom
Chancellor George Osborne is a distant 20/1, or a shorter 16/1 at Ladbrokes.
William Hill said that more than 20m was gambled on the referendum's result with fixed odds bookmakers.
"The result was profitable for our political punters," said William Hill spokesman Graham Sharpe, adding, "69 per cent of all the money we took was for Remain, but 69 per cent of all the individual bets were for Leave."