Supreme Court Justice Ruth Bader Ginsburg is an extraordinary woman, but Mimi Leder’s film about her early life is sadly ordinary. “On the Basis of Sex,” written by Ginsburg’s nephew Daniel Stiepleman (and thus carrying the subject’s imprimatur), covers her early years: her marriage, her education and her struggle as a lawyer in a decidedly male-dominated America, as well as her initial efforts to challenge the status quo. It’s an inspiring story, here told in a well-intentioned but thoroughly conventional made-for-cable fashion.

The film begins with Ruth (Felicity Jones) entering Harvard Law in 1956 as only one of nine women in the incoming class. All are invited to dinner with Dean Griswold (Sam Waterston), who smugly pontificates about their taking spots that could have gone to men. Professor Brown (Stephen Root) is no less condescending in class. But her supportive husband Marty (Armie Hammer), whom she met as an undergraduate at Cornell, encourages her to put up with the hassle, which she does even after he’s diagnosed with cancer and she takes up the task of covering his classes as well as her own, while also caring for their infant daughter. He survives against the odds, and they move to New York, where he takes a job in a law firm and she earns her degree at Columbia.

Despite exceptional credentials, however, Ruth cannot secure a position with a law firm and instead takes a teaching post at Rutgers, where she specializes in classes centering on gender discrimination. Urged by Marty—and her spunky daughter Jane (Cailee Spaeny)—she decides to take on a Colorado case in which the victim is a man, Charles Moritz (Chris Mulkey), who has been denied caregiver benefits by the IRS on the basis of his sex. She has to convince Moritz to hire her, and Mel Wulf (Justin Theroux, the head of the ACLU’s legal department, to join in the effort on his behalf.

The second half of the movie is devoted to the preparation of the case, which leads to Ruth and Marty arguing in a federal appeals court against an aggressive young lawyer (Jack Raynor) seconded by none other than Griswold and Brown. Much is made of how Ruth overcomes her initial hesitancy in addressing the court to deliver a stirring summation that sways the panel, inaugurating the string of cases through which she will chip away at barriers to women’s equality under American law.

Given the importance of the fight for women’s rights Ginsburg was instrumental in bringing to the fore, as well as the iconic status she has assumed in recent years, there should be as ready an audience of admirers for “On the Basis of Sex” as there has been for “RBG,” the documentary by Betsy West and Julie Cohen about her that found surprising success earlier this year. Even more than “Marshall,” Reginald Hudlin’s film about the young Thurgood Marshall, however, Leder’s movie seems airbrushed to a point of timidity, becoming a Ruth-and-Goliath tale with more than a hint of underdog cliché about it.

And the casting is a bit off. Jones is of the right petite stature, but frankly seems a trifle bland as Ruth, lacking the fizz and spunk of the genuine article, who makes a cameo appearance at the close, reminding us of the more rounded portrait even the affectionate “RBG” painted. Hammer, similarly, offers a quite generalized view of a picture-perfect husband who always sees his wife as an absolute equal, if not his superior. By contrast Waterston and Root ooze smugness, and Theroux and Kathy Bates, in a small role as feminist pioneer Dorothy Kenyon, come across at a very high pitch. Mulkey adds some shading to Ruth’s anxious client.

The picture is nicely appointed—Nelson Coates’s production design and Isis Mussendon’s costumes revel in period trappings, and Michael Grady’s cinematography gives the images a glossy sheen, though nothing really has a lived-in look; Michael Tesoro’s editing is nimble, moreover, and Mychael Danna’s score hits appropriately triumphant notes as needed.

In the end, though, “On the Basis of Sex” comes across as more hagiography than nuanced biography. Of course, that might not matter to Ginsburg’s legions of devoted admirers.