In 2002, MacDonell was a candidate for the leadership of the Nova Scotia NDP.[3] At the leadership convention in June 2002, MacDonell was defeated by Darrell Dexter.[4]
On June 19, 2009, MacDonell was appointed to the Executive Council of Nova Scotia, where he served first as Minister of Natural Resources until 2011. He then served as Minister of Agriculture. MacDonell was defeated in the 2013 provincial election.[2]