A Thai architect was pelted with cow faeces on Saturday in an unusual performance art piece inspired by an opposition party's controversial decision to form a coalition government with army-backed parties.

Thailand has endured months of political deadlock following May's elections, when the progressive Move Forward Party (MFP) triumphed only to be blocked from power by the kingdom's conservative establishment.

Former MFP partners Pheu Thai stepped forward to lead, forging an 11-party coalition with army-backed parties – including the Palang Pracharat (PPRP) party – despite a campaign pledge to never do so.

Ahead of the shock deal's announcement, well-known architect and artist Duangrit Bunnag had promised that "if Pheu Thai Party joins hands with PPRP, I will allow you all to throw faeces at me".

Clad in a hazmat suit and full-face mask, he made good on that promise on Saturday, kneeling on white tarpaulin in Bangkok's Lak Si district as people threw cow faeces at him.

"I want to communicate through art," said one anonymous poo-thrower, dressed in overalls and wearing an eerily realistic mask of PPRP leader Prawit Wongsuwan, before stepping up to slam Duangrit with dung.

The general was among the architects of 2014's coup, which removed Pheu Thai from power and installed a junta-backed administration that governed for the next nine years.

"Duangrit had faith in a political party, but that party wasn't taking their words seriously," the participant told reporters.

"Duangrit had to receive the poo on behalf of them."

Duangrit declined to speak to reporters – who warily pressed him for comment after he had been sprayed clean by an industrial hose.

"Only this will let me live in my life in the freedom to be, freedom to act," he said in a statement ahead of the show.

A medical team was on standby, with an ambulance whisking Duangrit away following the show. (AFP)