Abdulhameed Dashti received 11 years and six months for insulting Saudi Arabia and three years for insulting Bahrain in another case.
The outspoken lawmaker, who has been living overseas for the past four months, was also convicted of endangering Kuwait's diplomatic ties with the two countries.
Dashti, a strong supporter of Iran and Syrian President Bashar al-Assad, had told parliament that he was undergoing medical treatment in Britain.
The lawmaker still faces several similar cases and if convicted could receive additional jail terms.
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He denounced the 2011 Saudi military intervention in Bahrain to support the government against Shiite-led protests as an "invasion".
In May last year, Dashti filed a request to question the Kuwaiti foreign minister over the country's participation in the Saudi-led air campaign against Yemen's Shiite Huthi rebels.
But parliament refused to allow him to grill the minister over Kuwait's involvement, which he alleged was in breach of the constitution.
There are just nine Shiite MPs in Kuwait's 50-seat parliament.