Former Gujarat minister Jay Narayan Vyas, who resigned from the ruling Bharatiya Janata Party (BJP) earlier this month, joined the opposition Congress on Monday.
Congress president Mallikarjun Kharge inducted the 75-year-old minister into the party in Ahmedabad.
Rajasthan Chief Minister and Congress veteran Ashok Gehlot also welcomed Mr Vyas into the party.
Mr Vyas was a minister in the BJP government in Gujarat when Narendra Modi was the chief minister.
He resigned from the BJP on November 5.
Elections for the 182-member Gujarat Assembly are scheduled on December 1 and 5.