He has until April 20 to lodge an appeal.
Cairns sued Modi after he alleged on Twitter in January 2010 that Cairns was involved in match-fixing in the 2008 season of the rebel Indian Cricket League (ICL) while captaining the Chandigarh Lions.
Media law specialist Korieh Duodu told Newstalk ZB this morning the case highlighted that comments on social networking sites such as Twitter could potentially be defamatory.
"It's a significant ruling because the allegations were published ... in the form of a 140 character tweet and the court has found that this constitutes an actionable defamation and is one of the bases for awarding damages," he said.
Although the tweet would have been viewed by a relatively small number of people, the seriousness of the match fixing allegation justified the court's ruling, he said.
"One can see how even a small number of people might be an influential number of people."
"Given the tight-knit nature of the cricket community one can see how these allegations could cause a lot of damage," Mr Duodu said.
Cairns said he felt "mixed emotions" after he won the case.
"Firstly, sadness that I should ever have had to put myself, my friends and my family through this because of one man's misdirected allegations.
"But I also feel great joy because my past career has come through unscathed and remains intact and because I had the courage to stand up in the highest court to defend my name.
"Lastly, I feel great relief that I am able to walk into any cricket ground in the world with my head held high."
But Cairns may have a fight on his hands to get the money because Modi was recently declared bankrupt in a separate hearing over unpaid bills to a security firm.
Cairns, 41, was on a "no win, no fee" agreement with his lawyer. But Justice David Bean ordered Modi to pay 400,000 ($775,000) of Cairns' court costs within 28 days.
Cairns wasn't in London's High Court late last night when Justice Bean read his verdict.
Justice Bean said: "It is obvious that an allegation that a professional cricketer is a match-fixer goes to the core attributes of his personality and, if true, entirely destroys his reputation for integrity.
"The allegation is not as serious as one of involvement in terrorism or sexual offences [as in recent cases]. But it is otherwise as serious an allegation as anyone could make against a professional sportsman."
The judge said that Modi had "singularly failed" to provide any reliable evidence that Cairns was involved in match-fixing or spot-fixing, or even that there were strong grounds for suspicion that he was.
He described evidence from former ICL anti-corruption officer Howard Beer as "partisan to the point of being unprofessional".
Modi claimed Cairns conspired with former Indian international Dinesh Mongia to put pressure on younger players to underperform, and statements from players said they did so because they wanted to play.
During the trial, Cairns gave very animated evidence, at times slamming his glass of water on the bench while answering questions from the defence.
He said the "wholly untrue" claims left him angry and saddened.
"The defendant's allegations have also had a profound effect on my personal and private life. It put a strain on my marriage," he said.
It hurt him that his wife might think he wasn't the man she thought he was. "It hurts me, too, that friends _ many of whom are former cricketing foes _ will question my integrity as a man and a sportsman and that all I achieved in the great game of cricket is dust."
