Facing off before the Supreme Court on Wednesday, in what could be the most momentous abortion case in a quarter-century, will be two lawyers who are still in their thirties and are described by colleagues as whip-smart masters of the law and unflappable under pressure.

Arguing in defense of Texas’ sharp restrictions on abortion clinics will be Scott Keller, 34, the state solicitor general. He spent his childhood in rural Wisconsin, clerked for Justice Anthony M. Kennedy in the Supreme Court and was legal counsel in the Senate to Ted Cruz, whom Mr. Keller calls a mentor.

Speaking on behalf of Texas abortion providers, who are challenging laws that may force many clinics to close, will be Stephanie Toti, 37, a lawyer with the Center for Reproductive Rights in New York. Born in Brooklyn to an Italian-American family, she said her devotion to women’s rights was influenced by her grandmother, whose immigrant parents pulled her from school after the eighth grade because they feared that education would make her unmarriageable.

Ms. Toti has never argued before the highest court, but she is an experienced appellate advocate who, through the ups and downs of the Texas case, has dazzled her clients with intricate knowledge of the facts and an instinct for constitutional strategy.