The mayor announced his campaign at a Wednesday afternoon news conference. McGinn, a former Sierra Club leader, was first elected in 2009.
While he alienated some with his opposition to the tunnel replacement for the Alaskan Way Viaduct, the mayor gained allies in minority communities.
He also scored points for helping to negotiate a deal with private investors to build a new sports arena in an attempt to bring the NBA back to Seattle following the departure of the Sonics to Oklahoma City.
McGinn said he would emphasize education, transportation and neighborhood safety in the upcoming campaign. Several high-profile candidates have already announced they'll challenge the incumbent, including state Sen. Ed Murray, City Councilman Tim Burgess and former City Councilman Peter Steinbrueck.