At a function held at Vidhan Bhawan in south Mumbai, Council Chairman Ramraje Naik Nimbalkar administered the oath to Thackeray and others who were elected unopposed to the Upper House on May 14.
They include Council Deputy Chairperson and Shiv Sena leader Neelam Gorhe, four candidates of BJP Ranjitsinh Mohite Patil, Gopichand Padalkar, Praveen Datke and Ramesh Karad, NCPs Shashikant Shinde and Amol Mitkari and Rajesh Rathod of the Congress.
The nine seats fell vacant on April 24.The 288-member Legislative Assembly was the electoral college for the biennial elections to the nine seats.
With this election, 59-year-old Thackeray, who is also the president of Shiv Sena, makes his debut as a legislator. He was sworn in as chief minister on November 28 last year and required to become a member of either House of the legislature before May 27. Thackeray's son Aaditya is a member of the Legislative Assembly and also a minister in the three-party alliance government led by him.