The Thai king has approved a decision to hold a re-run of the general election on 15 October, a government spokesman said.
Thaksin Shinawatra's Thai Rak Thai wanted an October poll
The previous poll was annulled due to concerns about its legitimacy.
The Democrat Party boycotted the poll, claiming that Prime Minister Thaksin Shinawatra was abusing his power.
Analysts were unsure whether the king would approve the new poll date because the courts are still considering legal cases relating to the April election.
Wish for normalcy
Mr Thaksin wanted a new poll in October, but he needed royal approval before the date was officially set.
He has now got his wish. The revered Thai king reportedly signed the election decree on Thursday before going into hospital for back surgery.
"The reason that the king signed the royal decree was because he would like to see the country return to normalcy soon," said government spokesman Surapong Suebwonglee.
But while the election date is now certain, little else is. Thailand's political system has been in limbo since the Constitutional Court annulled the poll in April because of the Democrat boycott.
Since then, claims and counter-claims have been filed in every direction, with both sides accusing the other of electoral malpractice.
The Democrats face charges relating to their decision to boycott the poll, while the ruling party Thai Rak Thai is accused of financing smaller parties in an effort to make the election appear more legitimate.
Both parties could technically be dissolved if these accusations are upheld.
While this is unlikely, correspondents say the case exemplifies just how complicated the situation has now become.