Thanathorn Juangroongruangkit of the Future Forward Party broke the law by holding shares in a media firm when he registered to run in March's elections, the constitutional court ruled.

He was stripped of his role as an MP.

Mr Thanathorn said the charges against him were politically motivated.

He had insisted that he sold his shares in the company - V-Luck Media - to his mother before he registered as a candidate, but the court said there was no evidence proving this.

Mr Thanathorn was not given a jail term or banned from running for public office as some of his supporters had feared.

Future Forward came third in the elections with 6.2 million votes, and Mr Thanathorn has since emerged as the main voice of opposition to the military-dominated government.

He has been a strong critic of the powerful army's role in coup-prone Thai politics. Although the recent election formally ended five years of military rule, Prayuth Chan-ocha, who led the 2014 military coup, was elected civilian prime minister.

The military had been criticised for taking steps to ensure it would remain influential, including changing the constitution in 2017.

Future Forward has also dared to criticise Thailand's monarchy - which is protected by some of the world's strictest lese majeste laws.

In October, 70 Future Forward MPs voted against a royal decree transferring two army units to the direct control of King Maha Vajiralongkorn.