Somchai, the new prime minister, is the brother-in-law of Thaksin Shinawatra, Thailand's former leader, who was ousted in a 2006 military coup.
His appointment has not appeased the anti-government People's Alliance for Democracy (PAD) who accuse Thaksin of widespread corruption and have vowed to rid government of anyone connected to him.
Several of the most powerful ministries in Somchai's new cabinet - defence, the interior, finance and foreign affairs – have all been given to trusted Thaksin allies and close advisers.
Somchai replaced Samak Sundaravej, who was forced from office two weeks ago after Thailand's constitutional court ruled his hosting a TV cooking show while in office was a conflict of interest.
Samak's resignation had been demanded for weeks by PAD protesters, who accused him of acting as Thaksin's proxy.