The Constitutional Court ruled that Yingluck had a part in the transfer of Thawil Pliensri from the position of National Security Council secretary general and it was done in an unusual haste. (Agencies)
It said the transfer was done in only four days and there was discrepancy in dates of documents related to the transfer hence the process was irregular.
"Therefore her Prime Minister status has ended...Yingluck can no longer stay in her position acting as caretaker prime minister," presiding judge Charoon Intachan said in a televised ruling.
In the ruling, the court said Yingluck took part in the approval of the transfer.
Yingluck, 46, has argued that she assigned her deputy to take care of the issue so she did not take part in it. The court found nine ministers who were part of Yingluck's cabinet to be complicit in the decision and ordered them to be removed from their office.
The nine found complicit are - Deputy Prime Minister Pracha Promnog, Labour Minister Chalerm Yoobamrung, Deputy Prime Minister Plodprasop Suraswadi, Deputy Prime Minister and Finance Minister Kittiratt Na-Ranong, Deputy Prime Minister and Foreign Minister Surapong Tovichakchaikul, Prime Minister's Office Minister Santi Promphat, Information and Communication Technology Minister Anudith Nakornthap, Deputy Defence Minister Gen Yuthasak Sasiprapha and Deputy Commerce
Minister Siriwat Kachornprasart.
The Court ruled that it has no mandate to order the appointment of a new prime minister within seven days as requested by Senator Paibul Nititawan during the hearing of the case on Tuesday.
Paibul was the one who filed the abuse of power lawsuit against Yingluck.
The court ruled that only caretaker Prime Minister Yingluck and nine others who took part in Thawil's transfer must be removed from the cabinet.
The rest of members, who were not members of the cabinet that approved Thawil's transfer can remain in their office.
Yingluck assumed office as Thailand's premier on August 5, 2011.
Six months of political street protests have so far failed to force Yingluck from office, with anti-government People's Democratic Reform Committee (PDRC) demanding her resignation to pave the way for an appointed council that would institute reforms.
The Constitutional Court ruled that Yingluck had a part in the transfer of Thawil Pliensri from the position of National Security Council secretary general and it was done in an unusual haste.