Cullen has been with McGuireWoods LLP since entering practice in 1977. He was named chairman in December 2006, succeeding Robert L. Burrus Jr., and led the firm for 11 years. He is succeeded by Jonathan Harmon. As a partner in the firm, Cullen focuses on complex commercial litigation; government, regulatory and criminal investigations; white collar defense; and accountant defense. Cullen represented Mike Pence, the 48th vice president of the United States, in relation to Special Counsel Robert Mueller’s Russia investigation. He also advises Fred and Cindy Warmbier, the parents of University of Virginia student Otto Warmbier, in a wrongful death suit against the North Korean government. He represented then-FIFA president Joseph “Sepp” Blatter in relation to the investigation of FIFA by the Department of Justice and the Eastern District of New York. Cullen, along with former federal prosecutor and fellow McGuireWoods partner Toby Vick, negotiated an immunity deal with the U.S. Justice Department on behalf of businessman Jonnie Williams amid a federal investigation involving then-Virginia Governor Bob McDonnell. He led a successful bipartisan effort in 2013 to have Tracy Thorne-Begland seated on the Richmond General District Court Bench, making him the first openly gay judge in Virginia history. Cullen was the lead attorney for former U.S. Rep. Tom DeLay, R-Texas, during a six-year Justice Department investigation into alleged links between the congressman and former lobbyist Jack Abramoff. No criminal charges were filed against the former House majority leader. Cullen and fellow McGuireWoods partner Dennis I. Belcher represented Elin Nordegren in her August 2010 settlement with professional golfer Tiger Woods. In 2010, it was reported that Cullen was among the lawyers representing Bank of America in a multi-state investigation into the bank's foreclosure practices. Since joining the firm, Cullen has taken leave three times for public service assignments. In 1987, he served as special counsel to U.S. Sen. Paul S. Trible Jr., R-Va., during the Iran-Contra investigation. He was appointed by President George H.W. Bush in 1991 as U.S. Attorney for the Eastern District of Virginia, serving until 1993. In 1997, Virginia Governor George Allen appointed Cullen Attorney General of Virginia to fill the unexpired term of Jim Gilmore, who resigned to conduct a successful campaign for governor. In addition, Cullen was on President George W. Bush's legal team during the recount of the 2000 election in Florida.