He graduated from Lewis and Clark High School and attended Central Washington University in Ellensburg, where he earned a B.A.

In 1996, he was appointed King County Executive after the previous holder of the office, Gary Locke, was elected governor of Washington.

On February 2, 2009, President Barack Obama nominated Sims to become Deputy Secretary of the US Department of Housing and Urban Development, being confirmed by the United States Senate on May 6, 2009 and sworn in on May 8, 2009 [5] On June 14, 2011, less than two years after accepting his HUD appointment, Sims announced his resignation and intent to return to Seattle, citing a desire to spend more time with his family.

[10] However, a lawsuit filed by King County and a pro-growth management group prevented the referendum from being put on the ballot, and the state Supreme Court ruled that a state law requiring local governments to protect critical areas prevented local referendums from overturning critical area ordinances.

[11] On July 7, 2008, a Washington State Appeals Court found that the portion of the CAO known as the clearing and grading ordinance is an indirect and illegal "tax, fee, or charge", and that prior to restricting the clearing of land for lawn or pasture, King County must demonstrate how that act could cause harm.

[12] On May 16, 2005, Sims announced a controversial plan to purchase the 47-mile (76 km) Woodinville Subdivision railroad that runs through the east King County roughly parallel to Interstate 405 and replace most of its track with a bicycle trail.

[13] Although there is support for purchasing the railroad in order to prevent its current owner, BNSF Railway, from selling off the right of way piecemeal, the plan to remove the tracks has raised concerns from rail transportation advocates, environmental groups, and the owners, employees and customers of the popular Spirit of Washington dinner train (which ran on the tracks).

In 2007, the Port of Seattle, King County, and BNSF signed a preliminary agreement in which the Port would purchase the rail line from BNSF and then exchange the line plus $66 million to pay for removal of the tracks and replacement by a bicycle trail for Boeing Field[14] In July 2005, Southwest Airlines formally proposed plans to spend $130 million on a passenger terminal and other facilities and move the airline's operation from Sea-Tac Airport to Boeing Field after several months of negotiations with Sims.

In 2005, after further appeal by Yousoufian, the amount was increased to 15 dollars a day bringing the total to $122,000, plus a further $171,000 in attorneys’ fees, which some claim to be the highest such fine ever assessed in state history.