Ms Colvin - the only reporter from a British newspaper working in the opposition stronghold - died alongside French photographer Remi Ochlik when they came under fire from Syrian government forces.
A freelance photographer working for the Sunday Times, Paul Conroy, was also injured in the attack - he's understood to be in a stable condition.
Chris Ryder, a former Sunday Times staffer himself, said the veteran foreign correspondent would be greatly missed by colleagues and the wider world of journalism.
"She was one of the most distinguished of the modern generation of war correspondents," he told UTV.
"She was regarded by all in the journalism world as one of the bravest and most fearless and most perceptive of conflict reporters - it's a great loss.
Marie was an extraordinary figure, driven by a passion to cover wars in the belief that what she did mattered. She believed profoundly that reporting could curtail the excesses of brutal regimes and make the international community take notice.
John Witherow, Sunday Times editor
"I can empathise with the mood in the Sunday Times newsroom today - there'll be great gloom, great sadness, great sorrow and also great admiration for a colleague who brought such distinction to the paper."
Only on Tuesday, Ms Colvin had reported on the horrors unfolding in Homs and the relentless shelling of the city which has become a leading focus of unrest in the 11-month uprising against President Bashar al-Assad.
"I watched a little baby die today - absolutely horrific, just a two-year-old ..." she told the BBC.
"They stripped it and found the shrapnel had gone into the left chest. The doctor just said 'I can't do anything'. His little tummy just kept heaving until he died. That is happening over and over and over."
Describing the situation as "absolutely sickening", she added: "No one here can understand how the international community can let this happen, particularly when we have an example of Srebrenica - shelling of a city, lots of investigations by the United Nations after that massacre, lots of vows to never let it happen again."
Mr Ryder said the work by journalists like Marie Colvin put into perspective what he called "all the Leveson trivia".
"This is the real focus and this is the real purpose of journalism, this sort of work that she did - and the rest is all trivia by comparison." he said.
"Sad as it is, her death will underline the importance of brave and fearless journalism."
He added: "There's no doubt that war reporting is probably the most demanding and challenging of all the various tasks that any journalist can be asked to undertake.
"It's a very dangerous business and there are many, many risks and journalists often run those risks to report on these horrible events and these dreadful crisis and conflicts."
And Ms Colvin, who lost an eye in a grenade attack while working in Sri Lanka, was in no doubt about the risks.
Speaking at a 2010 memorial service for journalists killed reporting on conflicts around the world, she said: "Our mission is to report these horrors of war with accuracy and without prejudice.
"We always have to ask ourselves whether the level of risk is worth the story - what is bravery, and what is bravado. Journalists covering combat shoulder great responsibilities and face difficult choices.
"Sometimes they pay the ultimate price."
Journalists, politicians and human rights advocates - including Amnesty International - have joined in paying tribute to both Marie Colvin and Remi Ochlik.
"This is a desperately sad reminder of the risks that journalists take to inform the world of what is happening and the dreadful events in Syria, and our thoughts should be with her family and her friends," Prime Minister David Cameron said, during Prime Minister's Questions.
Marie and Remi died bringing us the truth about what is happening to the people of Homs. Governments around the world have the responsibility to act upon that truth - and to redouble our efforts to stop the Assad regime's despicable campaign of terror in Syria.
William Hague, Foreign Secretary
Bridget Jones author Helen Fielding, a close friend of Ms Colvin's, said in a statement: "Marie Colvin was the bravest and best of women, the most fearless and committed of journalists, and the dearest, most loyal and wildest fun of friends. I am so sad and so proud of her."
ITV News international editor Bill Neely said: "We were all, as a people, better for her.
"Her final dispatch was as deep as they come, in the 'widow's cellar' where women and children cower from Assad's assault and death feels imminent.
"At a time when journalists are being examined as never before, it's time to acknowledge someone who made a difference - a moral difference - to our country and our lives. That was Marie."
Sunday Times owner Rupert Murdoch also confirmed efforts were being made to rescue injured photographer Paul Conlon and said: "We are doing all we can in the face of shelling and sniper fire to get him to safety and to recover Marie's body."
It is estimated that at least 5,400 people, mostly civilians, have been killing in Syria as President Assad continues to crackdown on those involved in the uprising against his regime.