Labour MSP Helen Eadie has died at the age of 66.
It emerged earlier this week that she had cancer and was in a hospice at Queen Margaret Hospital, in Dunfermline.
She had been a Labour MSP since the parliament was established in 1999, as the member for Dunfermline East, and later as MSP for Cowdenbeath, following boundary changes.
She was diagnosed with her illness at the end of October.
She leaves a husband Bob and two daughters.
Scottish Labour Leader Johann Lamont said she was deeply saddened to hear of Mrs Eadie's death and described her as a "politician of tremendous passion and commitment".
She said: "Helen was very precious to her family. She played an important part in helping to establish the credibility of Holyrood.
"She will also be fondly remembered within the Scottish co-operative movement. Her commitment to delivering change in our communities was the essence of her political beliefs and values."
"She was her own woman who didn't fit the political stereotype. Perhaps that's why some underestimated her, but her difference was why she was admired by the people of her constituency.
"She will be missed by many and will be remembered across her constituency in standing up for their needs and concerns."
She added: "My thoughts and those of the whole Scottish Labour movement will be with Helen's family at this difficult time."
Former Prime Minister Gordon Brown, who is the MP for Cowdenbeath, described Mrs Eadie as a "passionate champion of social justice".
He said: "The whole of Fife is mourning the sudden and very sad death of our popular Member of the Scottish Parliament, Helen Eadie.
"Much loved and well respected throughout the county, Helen Eadie has spent her working life serving the people of Fife.
"Having spent many years as a Fife councillor Helen became, in 1999, the first member of the Scottish Parliament to be elected for the Dunfermline East and Cowdenbeath constituency, an area which she has represented with great distinction for 14 years."
Labour leader Ed Miliband said he was "deeply saddened". "A passionate, determined and committed MSP. She will be sorely missed," he wrote on Twitter.
First Minister Alex Salmond said: "My sincere condolences go to Helen Eadie's family, friends and colleagues. Helen served the people she represented diligently over the years, first as a Fife councillor and then as MSP for Dunfermline East and Cowdenbeath.
"Helen was also one of the Scottish Parliament's original MSPs first elected in 1999, and that unbroken 14-year period at Holyrood is a not inconsiderable record of public service of which her family can be rightly proud."
Willie Rennie, leader of the Scottish Liberal Democrats and MSP for Mid Scotland and Fife, said: "As fellow parliamentarians for West Fife, Helen's intense, burning commitment to socialism was inspiring to observe.
"Although a gentle and kind lady, you did not cross Helen without suffering from the sharp end of her tongue.
"Helen made waves for her causes and her constituents."
Scottish Conservative leader Ruth Davidson MSP said: "Helen was a committed parliamentarian and a true servant to her constituents in Fife.
"She was a wonderful, warm-hearted woman who would always go the extra mile to help someone out.
"She had friends across all parties, and Scottish politics is poorer for her passing."
Former First Minister Henry McLeish, who served with Mrs Eadie on Fife Council in the 1980s, said: "This is a sad loss for Fife. She was always a courageous, defiant and independent advocate for her constituents which is the highest compliment that can be paid to an elected representative."
Mrs Eadie recently campaigned in Labour's successful bid to win the Dunfermline by-election.
She has a union background and joined Labour in the 1960s, holding a number of posts in the party before life as an elected member beckoned.
She served on various Scottish Parliament committees over the years, but in June 2007 resigned her membership of two of them in protest at the Conservatives being given convenership of the equal opportunities committee.
At the time Mrs Eadie said the move was like "putting Attila the Hun in charge of care in the community".
Trapped in car
In November 2006 Mrs Eadie called for curfews for people under the age of 15, after she was trapped in her car by a gang of youngsters.
While looking into concerns from constituents about youth-related anti-social behaviour, she was surrounded by a mob in Cowdenbeath who started rocking the car and throwing missiles at it.
As a Fife MSP, Mrs Eadie called for an end to tolls on the Forth Road Bridge, during Labour's time in power.
In 2003, Mrs Eadie was the Labour group's most outspoken opponent to the then Labour/Lib Dem coalition's plan to introduce proportional representation (PR) in council elections.
Voting reform was a key part of the partnership agreement struck between Labour and the Liberal Democrats after the May election, but Mrs Eadie said it was an example of "the tail wagging the dog".
She said at the time: "It's about one of the smallest parties in the parliament wanting to use the power that they have to try to force through issues that they want to see steamrollered through."