"I accept the responsibility you have reposed in me. You will never get an opportunity to look down on what my government will do," he said in a 30-minute speech after he was unanimously elected the leader of the BJP Parliamentary Party by the newly-elected Lok Sabha members and those of Rajya Sabha.
The election took place at the Central Hall of Parliament after his name was proposed by senior leader L K Advani and seconded among others by Murli Manohar Joshi, Sushma Swaraj, Venkaiah Naidu, Arun Jaitley and Nitin Gadkari.
"A new hope has arisen in the common man. This is the biggest significance of this election results. At the end of the day for whom is the government It is for the poor.
"The new government will dedicate itself for the poor, crores and crores of youth and for the safety and security of the mothers and sisters, those in the rural areas, oppressed and the deprived," he said.
Referring to the nature of the verdict, he said if it had been a hung or a fractured verdict then one can say that people had vented their anger against the government and that it was anti-establishment.
"But by giving BJP an absolute majority they have voted for hope and trust. People have voted for hope and faith. And I will do everything to fulfil their aspirations," he said, adding that he is a man full of optimism.
There should be no room for pessimism and because with pessimism nothing can be achieved.
Recollecting an earlier speech of his, he said his government's motto will be with everyone and for everyone's development. "This is the time for new hope and strength."
Modi said in 2019 he will meet the MPs again with a report card. My government is not for myself but for the country. The government is for the poor and we want to do something for them, he said.
"I will strive my best to fulfil the responsibility you have reposed in me. You will never have to look down on the work it will do."
The PM-to be also took the opportunity to praise the work of the past governments, saying every government and its leaders have contributed to the welfare of the country and we will carry forward whatever good they have done.
Invoking former PM and BJP leader Atal Bihari Vajpayee, Modi said it would have been an icing on the cake had the ailing leader been present among them today.
As BJP leaders clapped and cheered, he said an era of responsibility has begun as people had high expectations from them.
During his acceptance speech, 63-year-old Modi broke down when he referred to L K Advani's mention that he had done favour to the party by taking up the responsibility.
"Can serving the mother be a favour A son is only dedicated to serve the mother....The favour has been done by the party," he said addressing the newly-elected MPs of the party in the historic Central Hall of Parliament.
Referring to his humble background, Modi said it was an ode to Indian democracy and its founding fathers that he was standing there, all set to be the new PM.
He asked party MPs to work with all purity not for designations but for the people of the country. "We are here in the temple of democracy. We will work with all purity... not for the designation but the people of the country. Work and responsibility are the biggest things."
Recalling his hectic campaign, he said every speck of his body and every moment of his time was dedicated to fulfil the responsibility BJP had given by making him its prime ministerial candidate on September 13 last year.
Modi said he reported to party president Rajnath Singh after the campaigning for the elections was over on May 10 and will similarly report to MPs, party and the country about the work of his government in 2019.
"I want to assure people that there is no need for pessimism and they should not go by the past bad experience.
The country has huge potential. If all countrymen take one step, the nation can move forward by 125 crore steps," he said.
It was for the first time he entered the Central Hall of Parliament and he recalled that he had seen the CM's office and a state Assembly for the first time after he was made Gujarat CM in 2001.