The 41-year-old all-rounder had sued Lalit Modi, the former Indian Premier League (IPL) commissioner, over the 25-word tweet posted in January 2010.
Cairns was not at London's High Court for the ruling by Justice Bean, who heard the case without a jury, the UK's Press Association reported.
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 added: "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 judge had heard that although less than 100 people had read the tweet, it had been picked up by cricket website Cricinfo.
When Cairns complained, Cricinfo withdrew its report, paid damages and apologized - but Modi declined to apologize and pleaded justification, maintaining that the charge was true.
Cairns's case was that it was "wholly untrue" and a very grave libel, which could destroy all he had achieved over a 20-year career.
In evidence, he said: "The defendant's allegations have also had a profound effect on my personal and private life.
"It put a strain on my marriage. It hurts that my wife may think that I am not the man she thought I 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." In 2007 and 2008, Cairns captained the Chandigarh Lions in the Indian Cricket League (ICL), which is now defunct after the IPL prospered instead.
The allegation made by Modi related to the ICL between March and April 2008 and October and November that year.
Cairns left the team in October 2008 for what was officially explained as a failure to declare a pre-existing ankle injury.
The libel trial followed the jailing of three Pakistan test cricketers last year for spot fixing and the conviction of English county bowler Mervyn Westfield for corruption earlier this year.
