She was 61.
Ifill was most recently the moderator and managing editor of "Washington Week" and managing editor of the "PBS NewsHour."
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Journalists from across the world expressed their sorrow on social media.
RIP Gwen Ifill. Her voice and her way will be sorely missed.— David Muir (@DavidMuir) November 14, 2016
Ifill has more than 20 honorary doctorates from around the world. She graduated from Simmons College in Boston.
A former newspaper reporter, Ifill switched to television and worked for NBC News and PBS. She moderated two vice presidential debates.
She took a leave from her nightly show for health reasons earlier this year, never making public her illness. A week ago, she went out on leave again, taking her away from election night coverage.
Sara Just, PBS "NewsHour" executive producer, called Ifill "a standard bearer for courage, fairness and integrity in an industry going through seismic change."