[7] The U.S. deputy chief of mission in Russia, Elizabeth Rood, replaced Sullivan as the top U.S. diplomat in Moscow until a permanent successor was named.

[10] He then received a Bachelor of Arts in history and political science from Brown University in 1981 and a Juris Doctor from Columbia Law School in 1985.

[11] In 1991, Sullivan served as Counselor to Assistant Attorney General J. Michael Luttig in the Office of Legal Counsel of the United States Department of Justice.

He advises CEOs, general counsels, and other senior executives on U.S. sanctions and export controls, international trade disputes and regulation, and foreign investment in the United States, the Middle East, Russia, and other countries.

He has represented these clients before executive departments and agencies of the U.S. and foreign governments, as well as in litigation in the United States, where he has filed briefs and presented oral argument in courts across the country.The biography also discussed work on client business in Russia, Iran, Cuba and Iraq and "advising a multinational manufacturing company on security policies and risk issues in countries with a high threat of terrorism, violence, and political instability".

He was soon thereafter nominated by George W. Bush to serve in a permanent capacity and was sworn in on March 14, 2008, after confirmation by the United States Senate.

[15] In a letter to Deputy Secretary Sullivan, House officials wrote that they considered "the refusal to comply with a duly authorized congressional subpoena as obstruction of the lawful functions of Congress and of the impeachment inquiry.

[6] As a lifelong hockey fan, Sullivan sought to utilize his passion and knowledge of the sport as a diplomatic tool to engage with Russians during his ambassadorship.

[18] While it was initially reported that this request was presumed to precipitate the careful selection of a new ambassador, the Biden administration did not rule out asking Sullivan to stay on indefinitely.

[20] However, Sullivan left the post in September 2022, by which point his departure was described as "expected", but expedited by what the Associated Press said was a "family medical issue".

[8] On September 5, 2022, Sullivan stated that his wife had died from cancer, and that was the reason for his return to the U.S.[21] In April 2021, after President Biden announced a new package of sanctions against Russia, Sullivan was summoned to a joint meeting between Vladimir Putin's North America adviser Yuri Ushakov and Foreign Minister Sergei Lavrov.