He also said the poll results will work as a "stepping stone" for the 2019 general elections.
The chief minister was speaking at the Congress' plenary session here ahead of the Karnataka polls, the dates for which are yet to be announced.
"No one can stop Rahul Gandhi (Congress president) from becoming the country's prime minister after the next general polls," Mr Siddaramaiah said.
"It is going to be a secularism versus communalism contest (in Karnataka). The Congress is confident that under Rahulji's leadership, we will come back to power with a thumping majority in Karnataka.
"It will be a big boost and work as a stepping stone for the coming Parliamentary elections," he said.
The greater part of Mr Siddaramaiah's speech was on the welfare programmes undertaken in Karnataka.
Campaign for the upcoming Karnataka election is already underway with national leaders of the Congress and BJP canvassing in the state.
The H D Deve Gowda-led JD(S) is the other major party contesting the elections.