Brian Duperreault’s underwriting experience stands in contrast to his predecessor as CEO of American International Group Inc. and should serve him well as he seeks to complete the turnaround of the New York-based insurer, observers say.

Mr. Duperreault, a longtime insurance executive who worked at AIG in the 1970s and 1980s, was named president and CEO of AIG on Monday after several weeks of rumors that he would be offered the job.

As part of the deal to bring him back on board, AIG agreed to tighter bonds with his previous company, Hamilton Insurance Group Ltd. — including the purchase of Hamilton’s U.S. platform for about $110 million — made other payments to Hamilton and offered Mr. Duperreault a hefty compensation package.

Addressing AIG investors on Monday, Mr. Duperreault broadly outlined his plans for AIG.

“I’m very happy to be back at AIG as CEO, and I look forward to making AIG better than it has ever been,” Mr. Duperreault said. “In that regard, I recognize the value of the company’s multiline structure. I didn’t come here to break the company up. I came here to grow it.” 

Activist investors, led by Carl Icahn, had previously pushed for the breakup of AIG. On Twitter on Monday, Mr. Icahn said he was pleased that AIG’s “board is finally making some of the much-needed changes we’ve been advocating the last 18 months.”

Mr. Duperreault said he would focus on underwriting discipline and that his “priorities include a commitment to technology.”

“Brian is uniquely qualified to lead AIG at this important time,” AIG Chairman Douglas M. Steenland said in a statement Monday.

Noting that Mr. Duperreault has spent his entire career in insurance, he added: “He is a hands-on leader who has consistently delivered strong bottom-line results. He has demonstrated a passion for deploying new and innovative ways to serve clients. All of this will enable Brian to help AIG achieve its full potential to be the leading insurance company.”

Mr. Duperreault, 70, an actuary by training, spent more than 20 years at AIG, rising to lead American International Underwriters, which comprised the insurer’s overseas operations. In 1994, he left to head Bermuda-based Ace Ltd. and transformed it into a multinational insurer. He retired from Ace in 2006 but came out of retirement in 2008 to lead Marsh & McLennan Cos. Inc. and helped turn around the brokerage, which was still recovering from the crisis triggered by the broker commission and bid-rigging investigations of then-New York Attorney General Eliot Spitzer. He retired from Marsh & McLennan at the end of 2012. Less than a year later, he came out of retirement again to lead Hamilton.

Mr. Duperreault will succeed former AIG CEO Peter Hancock, who announced in March that he would resign following a nearly $3 billion fourth-quarter 2016 loss. AIG recently bounced back from the loss, reporting a $1.19 billion profit for the first quarter of 2017. Mr. Hancock was named CEO of AIG in September 2014, having previously run the insurer’s property/casualty unit, but prior to AIG he had spent most of his career in the banking sector.

James Auden, managing director at Fitch Ratings Inc. in Chicago, said Mr. Duperreault seems a logical choice for AIG, noting “his stature in the industry and the history of success.”

“He’s had a very impressive career,” Mr. Auden said. “You could see perhaps more of an underwriting background was something they were looking for, and he definitely has that in his previous positions. And AIG has some unique issues with recent underwriting experience.”

Brett Horn, senior equity analyst with Chicago-based Morningstar Inc., wrote in an investment note Monday that Mr. Hancock’s lack of underwriting experience “seems like the most likely reason he was unable to effectively change the underwriting culture at AIG.”

While Mr. Hancock’s strategy was sound, he struggled in executing a turnaround in the underwriting culture within commercial property/casualty lines, Mr. Horn said. AIG has faced adverse development issues in several lines since its near-collapse during the financial crisis.

“We believe underwriting discipline is the key stewardship factor in the insurance industry, and pre-crisis management’s focus on growth is the root cause of AIG’s poor historical performance,” he wrote.

While AIG, which previously sold several of its units to help repay government bailout funds, is significantly different to the firm that Mr. Duperreault left in 1994, Caribou Honig, chairman and co-founder of InsureTech Connect in Richmond, Virginia, and co-founder of venture capital firm QED Investors, said Mr. Duperreault “knows exactly what he’s getting.”

“I’ve got to believe that he will look to bring in agents of change on the talent side,” he said.