Nasser Abul, 26, was found innocent of a charge related to threatening "state security", an offence that can carry a lengthy prison sentence.
However, Mr Abul was found guilty of contempt of religion and sentenced to three months in jail. Because Mr Abul has spent 111 days in custody since his arrest, his family were expecting him to be released from prison last night.
"He will be free today; this is a victory for freedom of speech," said Mr Abul's brother, Hassan Al Shirazi, 20, one of about 20 family members and supporters in court.
Mr Al Shirazi said when his brother is released he will take him home to "clean him up" before they attend a welcome-home gathering with family and friends at his lawyer's diwaniyah, the Kuwaiti equivalent of a Majlis.
Posts that appeared on Mr Abul's Twitter account in May called the Saudi king scum and compared Bahrain's royal family to Jews and pigs.
Mr Abul's lawyer had argued in court that his client's Twitter account had been infiltrated by hackers.
One of the detained man's supporters, Jaffar Ameer, speaking outside the court, said: "We don't agree with the second part of the judgement," referring to the three-month sentence for insulting Salafis. Mr Ameer argued that Salafism is a political rather than religious movement.
"The court accepted Salafism as a religion, so you cannot talk about them, you cannot say anything," Mr Ameer added.
The tweets were posted at a time of heightened sectarian tension in the Gulf after Bahrain's Sunni royal family cracked down on protests led by the country's Shiite majority.
While the majority of Kuwaitis are Sunni, between 15 and 30 per cent are Shiite.
Mr Abul was pictured on a Facebook page set up by his reporters at a demonstration in Kuwait to show support for the Bahraini opposition before his arrest in June.
Some Shiites claim that Saudi Arabia, which sent troops into Bahrain to help contain the anti-government protests, is wielding its influence in Kuwait through Sunni tribes with cross-border connections. They believe the Saudi government put pressure on the Kuwaitis to detain Mr Abul when the comments appeared online.
The case attracted international attention. Amnesty international said the posts did not advocate "violence, racism or racial hatred" and described Mr Abul as "a prisoner of conscience".
Twitter has quickly grown in popularity in Kuwait, which is home to the Arabian Peninsula's most influential parliament and a vibrant and critical press. The growth in the use of social media has recently led to a wave of court cases.