Welsing was admitted Thursday to MedStar Washington Medical Center in northwest D.C., reportedly being kept alive by a ventilator until her sister Loren Cress Love arrived from Chicago.
Donna Brazile, a stalwart on the D.C. political scene, said Welsing died of complications from a stroke she suffered earlier in the week.
Her death was quickly mourned by close friends on social media cites.
"RIP to the elder, Dr. Frances Cress Welsing, the inspiration behind 'Fear of a Black Planet,'" tweeted Chuck D, the leader of rap group Public Enemy, referring to the group's groundbreaking 1990 album that is viewed as one of the greatest and most important recordings ever.
Designer InI Vibez paid homage to the "great teacher and leader."
"I give thanks for all the powerful word sound and knowledge she has shared. Let us learn from the teachings of this divine queen and move accordingly," the designer wrote.
Born in Chicago on March 18, 1935, Welsing is noted for her "Cress Theory of Color Confrontation," which explores the practice of white supremacy.
In 1991, she authored the book, "The Isis Papers: The Keys to the Colors," where she states that a system is practiced by the global white minority, on both conscious and unconscious levels, to ensure their genetic survival by any means necessary.
Welsing said this system attacks people of color, particularly people of African descent, in the nine major areas of people's activity: economics, education, entertainment, labor, law, politics, religion, sex and war.
She said it is imperative that people of color, especially people of African descent, understand how the system of white supremacy works in order to dismantle it and bring true justice to the world.
Welsing appeared in the 2005 documentary, "500 Years Later," and the 2011 film, "Hidden Colors: The Untold History of People of Aboriginal, Moor and African Descent."
Dr. Benjamin F. Chavis Jr., president and CEO of the National Newspaper Publishers Association (NNPA), praised Welsing and her legacy.
"May God bless the living legacy and memory of freedom fighter Dr. Frances Cress Welsing. On behalf of the National Newspapers Publishers Association, we mourn the passing of our beloved sister and freedom fighter," Chavis said in a statement. "More than anyone else in the 20th and 21st centuries personified the intellect and courage to speak the truth about the pseudo-ideology of white supremacy and its longstanding impact on the consciousness and lives of millions of Black people throughout the world.
"Today we all must reaffirm our determination to keep the memory and legacy of Dr. Welsing alive in all that we do to continue to advance the struggle for freedom, justice and equality. RIP, Dr. Frances Cress Welsing."
Memorial services have not yet been announced.