Republic president Surangel Whipps Jr said the move was over the decision by other Pacific leaders to ignore Micronesia's request for their candidate to take up the role of secretary general of the forum.
For months, the regional body has been divided over whose candidate should get the forum's top job.
Former Cook Islands prime minister Henry Puna was appointed secretary general on Thursday, pipping Marshall Islands' diplomat Gerald Zackios by just one vote.
Whipps Jr told RNZ Pacific that the leaders' failure to honour an unwritten agreement that the role be rotated by sub-region was unacceptable.
"Today, we are sending a diplomatic note to Fiji to let them know that we are closing our embassy there because of the results of the forum and after our meeting, as president of the north Pacific, I believe we will make a joint statement and we will also be moving forward and removing ourselves from the forum."
Whipps Jr questioned the composition of the Pacific Islands Forum, and suggested a new regional body might be needed.
He said south Pacific countries dominate the forum's decisions by sheer numbers.
"For example, we have other islands in the north Pacific, we gave Guam, we have Saipan, we have Hawaii, we have American Samoa," he said.
"Why aren't they members of the Pacific Islands Forum? If we are allowing Cook Islands, Niue - which are part of New Zealand - to be part of the forum, to vote, then we should be allowing those other countries.
"As a region, as Pacific brothers, we will continue to fight for that, we will continue to be part of FFA, we will continue to be part of SPREP and all those things.
"But the PIF maybe we need to come up with a new organisation and find new members because the current configuration is self-interest and that is the problem."