Former Ontario attorney-general Michael Bryant knows his lawyers.

So when he selected Marie Henein to defend him against charges of criminal negligence and dangerous driving causing death, many outside the legal world were left wondering: “Who?”

But Toronto's top criminal lawyers say Ms. Henein is an obvious choice – a “lawyer's lawyer” and a formidable opponent who would be at the top of their lists, were they ever to find themselves facing criminal prosecution.

Osgoode Hall law professor Allan Young taught Ms. Henein when she was a student at the school and hired her to work on the biggest appeal of his career right after she graduated in 1989.

“I recognized immediately that she had talent,” he said.

Ms. Henein spent most of her career working behind the scenes at Greenspan Henein and White, where she was groomed by Edward Greenspan, arguably the most famous defence lawyer in the country, who has represented the likes of Garth Drabinsky, Karlheinz Schreiber and Conrad Black.

Ms. Henein was made partner in 1998 and began her own practice, Henein & Associates, in 2002.

Since then, Ms. Henein has worked on several of the country's highest-profile cases, including the successful acquittal of junior hockey coach David Frost, who had been accused of sexually exploiting some of his players.

Prof. Young said that much of the reason Ms. Henein remained out of the spotlight for so long is that Mr. Greenspan “overshadows everyone.”

But colleagues agree that Ms. Henein has also consciously chosen to avoid the limelight because she feels she can best serve her clients from behind the scenes. She has declined to grant media interviews since her selection by Mr. Bryant, turning down multiple requests from The Globe and Mail.

But Scott Hutchison, a former Crown attorney who has argued against Ms. Henein at least a dozen times, said that veteran Vancouver attorney Richard Peck, retained by Ontario's Ministry of the Attorney-General as prosecutor in the case, will be facing a formidable, confident and razor-sharp challenger.

“You're going to face a tenacious and incredibly prepared lawyer. … She'll just outwork you,” he said.

Toronto lawyer Phil Downes, a former Crown attorney who recently faced Ms. Henein in court, agreed that Mr. Peck should be prepared to go “up against the best.”

“You will be tested in every possible way. No stone will be left unturned,” he said. “Marie does not take any prisoners.”

Lawyers who have worked with Ms. Henein describe her as a brilliant and confident legal mind and workhorse who is respected by judges and immerses herself in the facts of a case.

She is especially adept, they said, at using case-specific evidence to argue her point, which will likely be key in Mr. Bryant's trial.

“She has a unique way of taking the facts of a case, understanding them and presenting them to a judge in a very compelling way,” said Michael Lacy, Ms. Henein's former legal partner, who has spent hours in her company discussing case strategy.

Mr. Hutchison said that Ms. Henein is an especially effective cross examiner, with a unique talent for reading witnesses and anticipating how they will react to questioning strategies.

But her no-nonsense, to-the-point style can also be “extremely intimidating” for witnesses, said Peter J.E. Cronyn, past president of The Advocates' Society, a position Ms. Henein will assume next year.

“I don't think any witness being cross examined by her would enjoy the experience,” he said.

And while Mr. Downes said some people might see her as too tough or abrasive, Mr. Cronyn points out that's not always a negative.

“For the purposes of doing what she's doing, warmth is not necessarily one of the qualities that you're looking for,” he said.