She worked in retailing after her graduation, and ran stores selling children's clothes in Clinton and Bayfield.

[1] In the 2003 provincial election she ran as the Liberal candidate in the riding of Huron—Bruce and defeated Progressive Conservative incumbent Helen Johns, a cabinet minister, by about 3,000 votes.

[2] On October 23, 2003, she was named parliamentary assistant to Steve Peters, the Ontario Minister of Agriculture and Food.

[3] In March 2006, Mitchell was named parliamentary assistant to David Caplan, the Minister of Public Infrastructure Renewal.

[6] On January 18, 2010, Mitchell was named Minister of Agriculture, Food and Rural Affairs as part of a cabinet shuffle by Premier Dalton McGuinty.