CONCORD, N.H. — At age 11, Jessica Grant used to turn her bedroom into a courtroom and play at being a lawyer.
She’s not playing anymore.
At age 44, she led the state of New Hampshire to a $236 million verdict last week against Exxon Mobil Corp. in a case about groundwater contamination from gasoline additive MTBE. It is the largest verdict by far in New Hampshire’s history and the largest of any MTBE case nationwide.
‘‘It was an extremely hard-fought case,’’ Grant said. ‘‘It was like doing hand-to-hand combat every day.’’
It was not her first dramatic courtroom victory.
In 2005, she secured a $172 million verdict on behalf of more than 116,000 Walmart workers who challenged the retail giant’s refusal to grant them breaks. In 2008, she successfully defended Intel Corp. against a $450 million breach of contract and patent claims case.
Three years ago, she was recruited by the San Francisco law firm of Sher Leff for New Hampshire’s MTBE case. Sher Leff has been at the forefront of many of the high-profile MTBE and water-pollution cases in the country.
She said she agreed to take the case on two conditions: She would bring in her own team of lawyers and paralegals and be allowed to significantly restructure the case. ‘‘We had to make it simple,’’ she said.
She pared the state’s lineup of expert witnesses from 17 to six. She narrowed the focus of the case from all wells with traces of MTBE to those at or above the maximum contamination level of 13 parts per billion. And she persuaded a Superior Court judge that it could be tried on a statewide basis rather than piecemeal.
For the past three years, Grant said, she has worked seven days a week, 10 to 12 hours a day.
Jurors, who sat through the three-month trial, delivered verdicts after just 90 minutes of deliberations.
Grant grew up in Orinda, Calif. Her father is an architect and her mother taught English and Latin and would not let Grant go out to play in the summer until she completed an essay assignment. She played on sports teams, including the Junior Olympics volleyball team.
‘‘I'm extremely competitive,’’ Grant said. ‘‘I love to win, and I hate to lose.’’