Washington's 1st congressional district encompasses parts of King and Snohomish counties.

Under current boundaries, Barack Obama swept the district in 2008 and 2012, with 60% of the vote each time.

Prior to the 2012 redistricting, the district encompassed part of Northwest Seattle and largely suburban areas north and east of Seattle, including Shoreline, Edmonds, Lynnwood, Mountlake Terrace, Kenmore, Bothell, Kirkland, and Redmond, as well as Bainbridge Island and part of the Kitsap Peninsula.

Soon after the 2012 general election polls closed, the Seattle Times and national news organizations called the district for Democrat Suzan DelBene, defeating Republican John Koster with a margin that the Seattle Times called "unexpectedly decisive",[6] reflecting the difficulty of predicting the vote in the new district.

[7] DelBene also won the election for the remainder of Inslee's term in the old first district, and after being sworn in on November 13, 2012.