Thailand's former prime minister Yingluck Shinawatra has been impeached, banned from politics and will be criminally charged over a failed rice subsidy scheme.

The military appointed Legislative Assembly has voted overwhelmingly to impeach Ms Yingluck, even though she was removed from power before last year's coup.

She has also been banned from politics for five years, ending any chances of a return once an election is held.

Ms Yingluck condemned the decision, describing it as the end of democracy in the kingdom.

"Democracy has died in Thailand today, along with the rule of law," she said in a statement posted on her Facebook page.

"That move to destroy me is still ongoing and I face it now."

The decision enraged the "Red Shirt" supporters of the Shinawatra family, but leaders warned against widespread street protests in a country where political gatherings are banned under martial law.

"Today's impeachment is the highest provocation, aimed at encouraging the Red Shirts to come out so they [the government] can shift the blame for all their failures onto the Red Shirts," Red Shirt leader Jatuporn Prompan told viewers on his Peace TV program.

"I asked the Red Shirt people to exercise maximum restraint ... these provocateurs will be disappointed. We still have a long way to go and after what happened to Yingluck, our hearts are awakened."

Former leader's failed bid to defend herself against impeachment

Ms Yingluck had earlier appeared before the country's parliament to defend herself against the impeachment proceedings.

The kingdom's first female premier and sister of former leader Thaksin Shinawatra was ousted from office by a controversial court ruling shortly before the army staged a coup in May.

In a rare public appearance, Ms Yingluck argued her case, saying there was no constitutional basis for her impeachment.

"The Constitutional Court has already removed me as prime minister," she told assembly members, saying she should not be impeached for violating a constitution that no longer exists under junta rule.

Ms Yingluck defended the rice scheme as an attempt to support Thailand's rural poor, who historically received a disproportionately small slice of government cash.

"I am not corrupt, I was never careless," she said.

The decision to impeach Ms Yingluck required three-fifths of the vote, or 132 of the 220 members of the Legislative Assembly.

A tally of votes placed on a whiteboard in the Legislative Assembly and broadcast live showed 190 members voted in favour of impeachment.

Earlier, the country's attorney-general Surasak Theerattrakul said Ms Yingluck would also face criminal charges over her role in the failed rice subsidy scheme.

"The attorney-general's office has considered witnesses and evidence submitted by the working team along with all witnesses and evidence from the National Anti-Corruption Committee and we agree that the case substantiates a criminal indictment charge against Yingluck," Mr Surasak said.

If found guilty, Ms Yingluck would face a maximum of 10 years in jail.

The decision will anger her supporters, known as the "Red Shirts", but with martial law still in place the military has warned against protests or violence.