SYDNEY, Australia — When Australia’s incoming prime minister, Tony Abbott, declared victory in the national elections held over the weekend, he pledged to swiftly enact the ambitious legislative agenda he had outlined on the campaign trail.

His conservative Liberal-National coalition would get to work scrapping the country’s unpopular emissions trading plan, crack down on the record number of asylum seekers arriving in Australia in dangerous boats and dump a tax on mining company profits on the first day of his administration, he told a crowd of triumphant supporters Saturday. Australia, he said, was once again “open for business.”

But Mr. Abbott, who during four years as opposition leader made his name as a ferocious opponent of the governing Labor Party’s agenda, now finds himself in unfamiliar territory, analysts say. The lawmaker known as “Dr. No” must learn to enact legislation, rather than simply criticizing it.

“He was probably the most negative, straight-for-the-jugular opposition leader we’ve ever had. And he was very effective at it,” Rod Tiffen, an emeritus professor of political science at the University of Sydney, said in an interview. “So it is going to be a challenge for him to put out this more positive image.”