The new MLC members were elected unopposed in the June 30 elections.
Former Chief Minister Jagadish Shettar, Karnataka Minister and Congress National Secretary NS Boseraju, and party leader Tippannappa Kamaknoor on Monday took oath as members of the Karnataka Legislative Council.
Chief Minister Siddaramaiah, Council Chairman Basavaraj Horatti, and Law and Parliamentary Affairs Minister HK Patil were among those present on the occasion.
The new MLC members were elected unopposed in the June 30 elections, as the opposition BJP and the Janata Dal (Secular) did not field candidates.
The three MLC seats had fallen vacant following the resignation of Baburao Chinchansur, R Shankar, and Laxman Savadi, who fought the Assembly elections in May.
While Mr Savadi won the election, Mr Chinchansur and Mr Shankar lost.
In the polls to the 224-member Assembly, the Congress won 135 seats, while the BJP secured 66 and the JD(S) 19.
Jagadish Shettar formerly headed the BJP government as chief minister for 10 months from July 12, 2012. He has also served as the leader of opposition in the Assembly as well as Assembly Speaker variously.
Ahead of the Assembly election, Mr Shettar joined the Congress after the BJP denied him a ticket.
He unsuccessfully contested the Assembly election from Hubli-Dharwad Central constituency on a Congress ticket.
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