President Barack Obama nominated Mandell as the U.S. ambassador to Luxembourg in June 2011. As with other political appointees who have not previously served in such posts, several media outlets noted that Mandell had no diplomatic experience and had been a prominent fundraiser for Obama; Mandell donated $30,000 to Obama's campaign and $50,000 to his inauguration committee in 2008. Mandell raised more than $200,000 for the 2008 Obama campaign and was one of two dozen bundlers that were nominated for ambassador positions. Mandell's confirmation hearing took place in September, and the
U.S. Senate approved his nomination by voice vote on October 18, 2011. He presented his credentials on November 16, 2011. Mandell's tenure was notable for the founding of the Luxembourg Forum, meetings between
United States Supreme Court justices and judges of the European Court of Justice, with the goal of identifying and working on legal issues where cooperation can provide a mutual benefit. In addition, during Mandell's ambassadorship the embassy worked with the government of Luxembourg to create a quarterly forum of U.S. business leaders, business leaders in Luxembourg, and officials of Luxembourg's government, with the intent of exploring opportunities for U.S. companies to expand in Luxembourg. Mandell resigned his ambassadorship in February 2015, saying it was time for him and his wife to return to private life in the U.S. On February 12,
Luxembourg Grand Duke Henri honored Mandell by naming him a Commander of the
Order of the Oak Crown an award that recognizes individuals for exceptional civil and military services. ==Later career==