Prior to his election to the Senate, Ranker served as San Juan County Commissioner. In 2011, he was appointed as an Advisor to President Obama's National Ocean Council. He is also the 2013-2014 President of Pacific Northwest Economic Region, a partnership of ten U.S. states and Canadian provinces.
Ranker was first elected in 2008, winning 58.6% of the vote against Republican Steve Van Luven. He was re-elected in 2012 with 62.9% of the vote, defeating Republican John Swapp.
Ranker lives on Orcas Island with his wife and daughter; his son serves in the U.S. Navy.