One of the most celebrated African-American broadcasters in the US was best known for moderating Washington Week in Review and for PBS NewsHour.
Ifill had been absent for last week's election coverage due to ongoing health issues and had been on leave since May.
"She was a journalist's journalist and set an example for all around her," said a PBS NewsHour executive producer.
"Gwen was a standard bearer for courage, fairness and integrity in an industry going through seismic change," said producer Sarah Just.
"She was a mentor to so many across the industry and her professionalism was respected across the political spectrum."
At a daily news conference, President Barack Obama offered his "deepest condolences" from himself and the first lady.
"She was a friend of ours, she was an extraordinary journalist, she always kept faith with the fundamental responsibilities of her profession," he said.
Ifill had moderated two vice-presidential debates as well as a Democratic primary debate last year.
In 2004 she moderated the debate between Dick Cheney and John Edwards, and in 2008 between Joe Biden and Sarah Palin.
Last year she hosted the primary debate between Hillary Clinton and Bernie Sanders.
Sarah Glover, the president of the National Associated of Black Journalists, expressed her condolences on Facebook, saying that Ifill "was a transformative voice among journalists".
In 2013, after being named co-host of PBS Newshour, Ifill told the New York Times that she hoped she would inspire future minority journalists.
"When I was a little girl watching programs like this - because that's the kind of nerdy family we were - I would look up and not see anyone who looked like me in any way. No women. No people of colour", she said.
Paula Kerger, president and CEO of PBS, said that Ifill's "contributions to thoughtful reporting and civic discourse simply cannot be overstated."
"She often said that her job was to bring light rather than heat to issues of importance to our society. Gwen did this with grace and steadfast commitment to excellence", Mrs Kerger added.
Before working in broadcasting, Ifill had worked as a print reporter for the Baltimore Evening Sun, the Boston Herald American, the Washington Post, and the New York Times.
She died after a battle with cancer.
Veteran journalist and news anchor Gwen Ifill has died aged 61, the Public Broadcasting Service (PBS) has said.