Parker Thomson's practice focuses primarily on complex commercial litigation ― including class action and multistate litigation ― corporate law, communications and media law, appellate litigation, environmental law, and the U.S. Constitution.

Parker regularly represents private and public clients, including the state of Florida. He has extensive experience representing clients before the U.S. Supreme Court, the U.S. Court of Appeals (11th Circuit), the Florida Supreme Court, and various state and U.S. federal courts throughout Florida. He presented oral argument before the U.S. Supreme Court in three cases and before the Florida Supreme Court in dozens of cases, and has been personally involved in over one hundred complex appeals involving issues such as the First Amendment to the U.S. Constitution, media law, environmental law, jurisdiction, sovereign immunity, and civil rights. He has substantial experience representing both private clients and the press concerning Florida's public records and sunshine acts as well as the U.S. Freedom of Information Act.

Parker's commitment to public service has earned him numerous awards for significant pro bono contributions, including providing volunteer legal assistance to the poor and other civic efforts. Parker joined Hogan & Hartson in the fall of 2001. Before that time, he practiced with a large firm in Massachusetts for two years before moving to Florida and establishing a boutique litigation firm that later became recognized as one of the top small law firms in the United States. Parker also headed the first law firm ever to achieve recognition from the Florida Supreme Court for its commitment to pro bono work.