French Polynesia's former president Gaston Flosse says he is in mourning because the French state has signed his political death by banning him from political office for five years for abusing public funds.

Flosse made the statement after France's highest appeal court upheld a 2020 conviction over a long-running abusive water supply arrangement in Pirae.

The ruling means Flosse won't be able to contest this year's French National Assembly elections and next year's territorial election.

As former and current mayors of the town of Pirae, Flosse and now President Edouard Fritch made the town administration pay for the water use in the upmarket Erima neighbourhood, where Flosse lived.

Flosse had set up the scheme and Fritch allowed the abusive billing process to be continued until the practice was discovered in an audit in 2011.

When the two were convicted in Tahiti in 2020, Flosse was declared ineligible to hold office for five years.

Flosse questioned how the justice system worked, as he was singled out for punishment in a witch hunt while Fritch got away with just a fine.

He said he wonders why Fritch wasn't made ineligible for two years because for years the scheme was run while Fritch was mayor.

Flosse's lawyer said he cannot understand the intellectual mechanism used to convict Flosse over the issue.

Losing the appeal in Paris this week, Flosse, who is 90, won't be able to run for office until 2027, but he said won't give up and continue with renewed vigour.

Only last week, he had announced his candidacy for one of the three French Polynesian seats in the French legislature.

In 2014, Flosse had been declared ineligible for five years after another corruption conviction and hoped to avert a renewed such sanction by taking the matter to Paris.

He was forced to relinquish the presidency to his deputy Fritch, but the two politicians have since fallen out.

Fritch has since been re-elected president and mayor of Pirae.

In French Polynesia, about a quarter of the ruling party's assembly members has corruption convictions, including the assembly president Gaston Tong Sang.