The gay rights champion's historic case led the US Supreme Court in 2013 to strike down the Defense of Marriage Act (DOMA), which denied federal benefits to married gay and lesbian couples.
While the ruling was limited to just a fraction of US states, it opened the door for a 2015 Supreme Court decision that same-sex couples had the constitutional right to marry nationwide.
"I lost my beloved spouse Edie, and the world lost a tiny but tough as nails fighter for freedom, justice and equality," Windsor's wife Judith Kasen-Windsor said in a statement.
"Edie was the light of my life. She will always be the light for the LGBTQ community, which she loved so much and which loved her right back."
Windsor was hit with a $363,000 estate tax bill after the 2009 death of her decades-long partner Thea Spyer, whom she had married in Canada.
Had the couple been straight, the tax bill would have been much less.
The situation mirrored that of countless others, who under DOMA were barred from federal recognition as spouses and therefore denied myriad benefits available to heterosexual couples.
"She will go down in the history books as a true American hero," said Windsor's attorney Roberta Kaplan.
"I also know that her memory will be a blessing not only to every LGBT person on this planet, but to all who believe in the concept of b'tzelem elohim, or equal dignity for all."
Windsor was born Edith Schlain in Philadelphia on June 20, 1929, to Jewish Russian immigrants.
"Her memory will be a blessing not only to every LGBT person on this planet, but to all who believe in the concept of b'tzelem elohim, or equal dignity for all" (Photo/Paulina Vidal) Source: Paulina Vidal
After a brief marriage to a man, she divorced and moved to New York, earned her master's degree and got a job as a computer programmer for IBM, and hid her sexual orientation from her colleagues.
Several years later, she met Spyer, with whom she stayed until her death.
The pair marched in Pride parades and joined activist gay and lesbian rights groups, but it was following Spyer's death that Windsor's judicial odyssey began - and ultimately cemented her status as a pioneer for civil rights.
Former president Barack Obama, whose time in the White House included both Windsor's victory and the full legalization of same-sex marriage, praised Windsor's hard-fought battle.
"Edie spoke up - not for special treatment, but for equal treatment - so that other legally married same-sex couples could enjoy the same federal rights and benefits as anyone else," Obama said.
"Few were as small in stature as Edie Windsor - and few made as big a difference to America."
