His daughter, Julie Guyot-Diangone, said he died Friday in Mount Rainier, Md.
At the age of 25, Guyot worked with the Student Nonviolent Coordinating Committee and later became founding chairman of the Mississippi Freedom Democratic Party, which lobbied for blacks to have the right to membership in the Democratic Party, The Washington Post said.
For his efforts, he endured a severe beating in 1963 Winona, Miss., and he and other activists were jailed.
In a 2007 interview with the Post, he said he was beaten from head to foot. Guyot said a jail guard took him outside to show him to a group of white men and told them, "Now you know what he looks like."
Eleanor Holmes Norton, the District of Columbia's delegate to the U.S. House of Representatives, called Guyot "an unsung hero." She said she met him soon after the 1963 beating.
"Very few Mississippians were willing to risk their lives at that time, but Guyot did," she said.
Guyot was born July 17, 1939, in Pass Christian, Miss., and graduated from Rutgers University law school in New Jersey in 1971.
Besides his daughter, he is survived by his wife, Monica Klein Guyot, and son Lawrence Guyot III.