On February 22, 2017, McCullough was traded, along with Bojan Bogdanović, to the Washington Wizards in exchange for Andrew Nicholson, Marcus Thornton and a 2017 protected first-round draft pick. On March 1, 2017, he made his debut for the Wizards, making just one free throw in 1:39 of action during a win over the Toronto Raptors. Two days later, he was assigned to the Northern Arizona Suns of the NBA Development League, pursuant to the flexible assignment rule. He remained with Northern Arizona until the end of the 2016–17 D-League season.