"Give Bihar special status now, else after 2014 you will have to give it for sure. Only those will be allowed to rule Delhi who take care of the backward areas," Mr Kumar told an energetic crowd of an estimated 50,000 people at his Adhikar rally on the Ramlila grounds.
Lok Sabha elections are due only next year, but the Janata Dal (United) or JD(U) leader's statement appears to be sensitive to the political scenario that may emerge after the 2014 polls. The JD(U) is a key member of the BJP-led National Democratic Alliance, but is averse to Narendra Modi, whom many in the BJP have been pitching as the coalition's ideal prime ministerial candidate.
The JD(U), which did not invite the BJP for today's rally, has in the past threatened to walk out of the NDA if Mr Modi is made the prime ministerial candidate. Speculation about the JD(U) warming up to the Congress has also been in the air often.
Mr Kumar said Bihar has been treated unfairly by successive union governments and the time has come to give the state its dues. "Bihar is way below the national average in all development indices, such as roads, power, railways and per capita income. Don't the people of Bihar have the right to a better life?" he asked. (Read: Highlights of Nitish Kumar's speech)
"The youth of Bihar is forced to migrate to Delhi and other cities for jobs. We are not beggars. Development is the right of our people," the JD(U) leader said as party activists, waving flags and placards and wearing T-shirts embossed with his photo, cheered.
Mr Kumar will meet Prime Minister Manmohan Singh on Monday to raise the demand for special status. The two leaders have met several times on the issue.
"Our fight is not only for Bihar, but for all backward states. The Prime Minister has praised the growth that Bihar has shown in recent years. If we get special status, we can contribute more to the country's growth rate," he said.
Today's rally is being seen by many as Mr Kumar's show of strength as a development mascot and a counter to Narendra Modi, who has billed his third consecutive election win in Gujarat last December to his state's development.
But JD(U) chief Sharad Yadav denied any power play, saying: "A rally that is linked to the welfare of 10 crore people of Bihar cannot be called a show of strength."
N K Singh, the party's member in the Rajya Sabha, told NDTV: "This is a big day for Bihar's development initiative and for Nitish Kumar in moving away from identity-based politics to development-based politics. There is no political colour to this rally."
Get the latest election news, live updates and election schedule for Lok Sabha Elections 2019 on ndtv.com/elections. Like us on Facebook or follow us on Twitter and Instagram for updates from each of the 543 parliamentary seats for the 2019 Indian general elections.