Yingluck Shinawatra waves to supporters as she leaves the Supreme Court in Bangkok on Aug.1, 2017. AFP

Yingluck, who ruled from 2011 until she was ousted in a 2014 military coup, was charged with malfeasance in a 2013 project worth over $6.7 million (240 million Baht). The ruling is the latest legal success for the powerful Shinawatra family after Yingluck's brother Thaksin — a two-time premier also ousted in a coup — was freed on parole in February, six months into what was originally an eight-year prison sentence.

Yingluck and five others were accused of not running a proper bidding process to run the "Roadshow to Build the Future of Thailand," a campaign to promote her government's infrastructure projects.

Nine judges sitting in the kingdom's top court ruled unanimously in favour of the former premier, saying they "found no intention" to benefit the two major media outlets which won the contract, according to a statement. "The project was done according to the regulations," the court statement said.

Yingluck, who has lived in self-imposed exile since 2017 to avoid a conviction in another case, was not present at the court but was represented by her lawyer.

"We received the mercy from the court to dismiss the case," fellow defendant Niwatthamrong Boonsongpaisan, a former deputy PM, told reporters outside of court. "We are not corrupt," he added. It was the latest favourable verdict for Yingluck.

The Thaksin-backed Pheu Thai Party came to power last year after a general election in coalition with military parties connected to the coups that twice removed the family from power, and Thakin’s dugahter Paetongtran has since become the party’s leader and a prospective future prime minister.

Parties supported by Thaksin continued to reign at the polls after his ouster. However, last year, Pheu Thai managed just a close second-place election finish to the more progressive Move Forward party, whose proposals for reform of the army and the monarchy alarmed the royalist conservative establishment more than a return of Pheu Thai, which had softened its anti-military line and was anxious to get back into power.

Thaksin also remains in legal jeopardy despite his release. The Office of the Attorney General says it is still investigating a charge of royal defamation that was made against Thaksin almost nine years ago. He could face up to 15 years in prison if he is ever convicted.

Agencies