The NDP won a majority government under Bob Rae's leadership in 1990. McClellan served as a senior policy adviser to the Premier from 1990 to 1995. McClellan was privileged to attend and participate in all meetings of the Rae Cabinet, and was co-secretary of the Cabinet Planning and Priorities Committee. He influenced many key policy decisions, including the decision to raise welfare rates by 22% and to protect the rates from cuts, to maintain and expand Ontario's stand-alone social housing program, as well as the government's decision not to introduce public auto insurance in 1991.