William Barnes is one of a group of two political scouts who comes to visit Leslie Knope and offers to help her run a City Council election campaign.
William Barnes and Elizabeth first show up at the end of the episode "Li'l Sebastian" to tell Leslie they think she'd make a good candidate for public office. They ask her if she has any scandals in her life that could ruin her campaign. Leslie glances at her boyfriend Ben Wyatt and then back to the political scouts, and tells them she doesn't have any scandals in her life.
William, along with Elizabeth, works alongside Leslie to help her with her campaign for city council. In "Citizen Knope", Leslie gives them both Christmas presents. She presents William with a Knope 2012 Christmas ornament. She attempts to give Elizabeth a menorah, but Leslie is then informed by Elizabeth that she is not Jewish, and instead receives a Christmas ornament as well. After Leslie and Ben admit to having had a relationship together, William and Elizabeth tell her that they have to resign as her political advisors. They inform her she is polling at only 1% and can no longer advise her. William and Elizabeth's final appearance is in "The Comeback Kid", as they inform Leslie when they run into her at the Pawnee City Hall that they're searching for other political candidates.