Senior Congress leader Dinesh Gundu Rao on Wednesday assumed charge as President of its Karnataka unit at a massive rally at the Bengaluru Palace grounds.
Party President Rahul Gandhi had on July 4 appointed Rao to the post.
The party's new Working President Eshwar Khandre also took charge with Rao.
Deputy Chief Minister G. Parameshwara, who has been the party's president since 2010, resigned in line with its policy of holding one post.
Rao, 48, is a four-time MLA from Gandhinagar assembly constituency in Bengaluru central and second son of former Congress Chief Minister R. Gundu Rao.
"By appointing Rao and Khandre as the party's state unit president and working president, Congress has shown belief in the youth and commitment to stand for them under their leadership. I have confidence they will uphold the party's legacy," tweeted Parameshwara.
Addressing the party's state leaders and hundreds of cadres who gathered from across the state, Rao said the Congress had sacrificed to form a coalition government with its arch rival Janata Dal-Secular (JD-S) to protect secularism and democracy and prevent "communal forces" from ruling.
"Though the party won 80 of the 224 seats (in the May 12 assembly elections) as against 36 by the JD-S, we have agreed to support it in forming the government for achieving our objectives at the state and national levels," he said.
The JD-S and Congress formed a post-poll alliance and came to power on May 23, with HD Kumaraswamy of the JD-S and Parameshwara assuming office as Chief Minister and Deputy Chief Minister respectively after the three-day BJP government fell in the absence of majority on May 19.
Claiming that Prime Minister Narendra Modi would not return to power after the 2019 general elections, Rao said the BJP had no base in the south barring Karnataka, while the ground situation in the north was changing against both.
"A Congress-led government will be certainly formed in the centre with Rahul Gandhi as the Prime Minister," he told the gathering to thunderous applause.
He also vowed to make his party win all the 28 seats in the Lok Sabha from the southern state.
Cautioning the cadres from working against the party, Rao exhorted them to observe the ethics of coalition in the interest of the state and its people.
"I will not spare anyone who damages the party's reputation. Ministers too should not talk out of turn but maintain party's unity," he said.