Barra, a 33-year GM veteran who turns 52 on Christmas Eve, was marked for future success in the company's "Progression and Succession" reviews, annual surveys designed to identify young high-potential employees, former GM executives said.

"She was always at the top of that list" in the late 1990s, said Don Hackworth, who retired as head of GM's North American Car Group in 2001.

Barra's early identification as a "high-pot" executive led to a job in the corporate suite, as Vice Chairman Harry Pearce's assistant, when she was still in her 30s.

"It was a great opportunity to get an overview of how the corporation works," said Michael Losh, GM's former chief financial officer.

Barra's long tenure at GM - the Michigan native started as an 18-year-old engineering intern at Pontiac, where her father was a die maker for nearly four decades - might have raised suspicions that she was too much a part of the old regime, which was forced to seek bankruptcy protection and a U.S. government bailout in 2009.

But "she wasn't part of the established order that destroyed the company," said a Wall Street investment banker who has worked with GM for decades. "She's the best of the 'old GM' and she's a pretty modern thinker in terms of how to compete in today's world."

Former GM executive Lynn Myers, one of the first women in Detroit to run a car division before her 2004 retirement, said: "This is not business as usual at GM. It's not like the past. Mary is not afraid to shake the bushes."

Executives cite Barra's "radical" restructuring over the past two years of GM's sprawling and often dysfunctional global product development organisation.

"She does what she thinks is necessary to take action if something needs fixing," said Gary Cowger, GM's former group vice president who retired in 2010.

Barra, the mother of a teenage son and daughter, is described by those who know her as approachable, unflappable and inclusive.

"She can be under huge pressure and she just never loses her calmness," said a person close to Barra. "She thinks things through. When she speaks, I listen."

Neil De Koker, another former GM executive who sits with Barra on the board of Kettering University, said: "She has great people skills. She is easy to talk to and is an attentive listener.

"When she talks to students, you can tell she's a mom. And that's not the way you normally would describe the CEO of one of the world's largest manufacturing companies."

The person close to Barra described how she deftly handled the complicated and potentially traumatic overhaul of GM's engineering and development groups.

"You know how sometimes people come in and change things and bodies are left in the wake? That's not Mary. She might fire somebody (and) they'd be hugging her and thanking her.

"She talks a lot about how important winning the hearts and minds of employees is. I see her as a very motivational leader."

The issue of Barra's gender, she is the first woman CEO in a century-old industry that has been dominated by men, is mentioned frequently, but usually dismissed as the deciding factor in her promotion to GM's top job.

"These 'firsts' of women CEOs are no longer newsworthy," said Bonnie Baha, portfolio manager at DoubleLine Capital. "The focus should be on her qualifications, which appear to be uniquely suited to running GM."

Steven Rattner, the former head of President Barack Obama's task force who helped steer GM's 2009 bailout, said: "I have absolutely no doubt they picked (Barra) because she was the best person ... This company has been through so much that the idea that they would just do something to make history is unimaginable."

(Additional reporting by Ben Klayman, Deepa Seetharaman and Bernie Woodall in Detroit and Jennifer Ablan in New York. Editing by Andre Grenon)

By Paul Lienert