In one of the most sensational cases the NAACP Legal Defense Fund handled, Marshall saved the life of Lee Irvin, a Groveland, Florida black man. Irvin was wrongly condemned to death for supposedly raping a white woman. The alleged assault in 1951 set off a storm of white mob violence, which included burning down the homes of 400 black people in Groveland. Four black men were severely beaten during the riot; one died. Threats against him prompted Marshall to travel in the area with two bodyguards, and to spend every night and eat every meal in a different home.

This case demonstrates Marshall's prowess at using political pressure when he failed in court. Defendant Lee Irvin was initially sentenced to death. Marshall appealed all the way to the Supreme Court, which refused to consider the case. Along the way, Marshall generated local and international news stories about the case to build political pressure on Florida's governor. With Congress and the Justice Department also leaning on him, Governor LeRoy Collins eventually commuted the sentence to life in prison. Irvin was released several years later.