It comes after Bainimarama said the President Ratu Wiliame Katonivere had failed to protect the constitution and the rule of law in his opening statement for the 2023 parliamentary session.
The FijiFirst leader will be out of Parliament until 17 February 2026, after a midnight vote as both sides of the House clashed over Bainimarama's suspension, Radio New Zealand Pacific reported.
Leader of government business Lynda Tabuya said Bainimarama's words "denigrated" the head of state when he uttered "seditious words".
"Matters of offensive conduct towards Parliament must be taken seriously. It is even more important that members of parliament uphold the required standard of behaviour in Parliament," she said.
"In particular, the prohibition against speaking words that are disrespectful to our head of state as well as seditious words that breach the standing orders."
The Parliamentary Privileges Committee had recommended that Bainimarama be immediately suspended for three years; that he provide a written apology to the President within 14 days; and issue apology to public within 48 hours.
It also recommended that he not be allowed to enter Parliament during the period of suspension; and if he fails to comply then necessary enforcement measures will be implemented.
Co-deputy PM's Viliame Gavoka and Professor Biman Prasad supported the former PM's exclusion.
Gavoka said Bainimarama's comments were an "insult" to President Katonivere and his "ignorant comments can destroy confidence" in the office of the head of state.
He urged all MPs to "defend the values" of Parliament and "denounce the ignorance" of the leader of opposition.
Professor Prasad said Bainimarama was a "repeat offender of parliamentary assault" and his words were "utterly pathetic".
But PM Sitiveni Rabuka appealed to the Speaker Ratu Naiqama Lalabalavu and the parliamentarians as the "lone voice" from the government side for Bainimarama to be forgiven and he receive a lenient suspension.
Rabuka's plea resulted in the government side amending their motion to reduce Bainimarama's suspension to 18 months.
However, the opposition side did still not did not support the amendment late into Friday night.
"You cannot apologise if you have done nothing wrong," FijiFirst MP Jone Usamate said as he defended Bainimarama's political fate.
While another opposition member, Faiyaz Koya, said they "did not find any guilt" in what their party leader said.
Bainimarama becomes the fifth MP to be suspended from the House after breaching privilege.
Previously, the current Speaker Ratu Lalabalavu was suspended for two years in 2015 as a Sodelpa MP, former National Federation Party MP Tupou Draunidalo was suspended in June 2016 for the remainder of her term, and another Sodelpa MP Ratu Isoa Tikoca was suspended for two years in September 2016 while the current home minister Pio Tikoduadua was suspended for 6 months in 2019.
RNZ Pacific has contacted Mr Bainimarama for comment.