Marape. in his maiden speech in parliament, said he wanted PNG to be the "richest black Christian nation" on earth.
"Since my resignation as finance minister on April 11, I did it for my own reasons, some were personal pertaining to my district and province," he said.
He paid tribute to Peter O'Neill for his leadership over the past eight years.
"He held the ship under trying circumstances, amid many challenges - personal as well as national. Along the way, we may have differed a little bit, made mistakes a little bit, but he did his absolute best for our country."
"I pay my greatest respect to him. There is no greater love than a man who lays down his life for his country," he said.
Marape said the lessons learnt in the past few weeks culminated in his election. "These are lessons that some of us will take with us for a long time. Politics can come and go. But what we witnessed today transcends political boundaries, ethnic and cultural divide and religious views. Passing of the torch to me represents a shift of the torch to younger generation of leadership for our country."
He said the dynamics of what would have been a vote of no confidence changed through O'Neill's resignation.
"Today I stand before this nation and the honourable house, humbled but also burdened that the challenge is not easy," Marape said.