Emir Shaikh Jabir al-Sabah issued the decree that removed the current crown prince, Shaikh Saad al-Sabah, from the post of PM.
Shaikh Sabah al-Sabah, who is also the foreign minister and brother of Kuwait’s emir, was immediately appointed to take on the role.
A pro-liberal who favours privatisation and globalisation, the new PM is keen on improving Kuwaiti-Arab relations - even with those Arab governments that supported Iraq after it invaded Kuwait in August 1990.
Although the new parliamentary leader is the first person other than a crown prince to head the government in the oil-rich Gulf Arab state, he has already been the country's ruler in practice for many months.
Both the emir and the crown prince are seriously ill and all three men are in their seventies.
Time for change
The al-Sabah family has come under intense pressure, from within and abroad, to loosen its grip on government and share power – something the family has held since 1752.
However, the top post and other key government portfolios still remain in the ruling family.
Some parliamentarians, such as Ahmad al-Saadoun, have said the mere separation of powers is far from satisfactory to many reformists, who want a ceremonial role for the al-Sabah family and for the prime minister's job to be up for election.
But others, such as former speaker Jaasim al-Khurafi, predicted the decree last Tuesday, saying the separation of the two posts was a first step towards sought-after reforms.
Under Kuwait's constitution, the emir and crown prince are above censure, but anyone else serving as prime minister can be held accountable.