Phyllis Frelich fell in love with acting in the 1960s while attending Gallaudet College (now Gallaudet University), a Washington-based school for the deaf and hearing-impaired. After starring in campus productions, she decided to pursue a theater major.

But not only did the school not offer the discipline, educators there discouraged it. She was told repeatedly that there wasn’t a future in acting for deaf performers. She was persuaded to instead major in library science — a field, her adviser reasoned, that could serve her better as she followed any future husband around the country.

Despite that bleak start, Ms. Frelich became one of the most prominent deaf actresses of her generation.

Ms. Frelich, who helped found the National Theatre of the Deaf soon after her Gallaudet graduation in 1967 and won a Tony Award in 1980 for her leading role in the romantic drama “Children of a Lesser God ,” died April 10 at her home in Temple City, Calif. She was 70.

The cause was progressive supranuclear palsy, a degenerative neurological disease, said her husband, Robert Steinberg.

Phyllis Frelich and John Rubinstein, stars of the Broadway play "Children of a Lesser God,” in 1980. (Richard Drew/AP)

Ms. Frelich helped build the National Theatre of the Deaf in Waterford, Conn., into a nationally recognized company that pioneered productions in American Sign Language and spoken English.

Ms. Frelich starred in several National Theatre of the Deaf shows but was dismayed by the lack of parts for deaf actors in what she referred to as “the hearing theater.” An encounter with playwright Mark Medoff at a theater workshop at the University of Rhode Island changed her future.

Ms. Frelich was the first deaf person Medoff ever befriended, and he once told The Washington Post that he “became obsessed with wanting to learn her language.” The result was “Children of a Lesser God,” largely inspired by Ms. Frelich’s marriage to Steinberg, who had full use of his hearing.

“Children of a Lesser God” reached Broadway in 1980, with Ms. Frelich and John Rubinstein in the leading roles. It was about the romantic relationship between a deaf student and her teacher, a speech pathologist.

Medoff said he saw the couple’s barriers in communication as a broader metaphor for how people often interact, for better or worse. Ms. Frelich’s character is complicated — proudly stubborn and sometimes angry about having to learn to read lips and speak.

“Using no words at all, Ms. Frelich . . . creates a character of challenging complexity,” New York Times theater critic Walter Kerr wrote. “Severely private, sharply outspoken, wry, . . . sensually responsive, firmly determined to lead a life that is specifically hers.”

The show, which used American Sign Language and could be followed by both deaf and hearing audiences, received the Tony Award for best play as well as best actor and actress. It ran for more than two years.

The 1986 film version starred William Hurt and deaf actress Marlee Matlin, who won the best actress Academy Award. Steinberg said his wife did not get the movie role because she was in her 40s and the part called for a younger actress.

After the play closed on Broadway, Ms. Frelich moved to Los Angeles and received an Emmy nomination for her role as a deaf parent in the 1985 made-for-TV movie “Love Is Never Silent,” based on Joanne Greenberg’s 1970 novel “In This Sign.”

She starred in five other plays written by Medoff and performed in shows produced by Deaf West Theatre Company in the 1990s and early 2000s. She had a recurring role on the TV soap opera series “Santa Barbara” and guest-starred on TV programs such as “ER,” “Diagnosis: Murder” and “CSI: Crime Scene Investigation.”

Phyllis Annetta Frelich was born Feb. 29, 1944, on a farm near Devils Lake, N.D. Both of her parents were deaf, as were eight younger siblings. Her mother was a seamstress and her father a typesetter.

Ms. Frelich, who graduated from the North Dakota School for the Deaf in 1962, said she did not consider deafness a handicap. “It was like having brown hair; I never questioned it,” she told the New York Times. “I have nothing to compare my silence to. It’s like you can’t ask a child to draw a picture of a fire engine when he’s never seen one.”

Besides her husband of 46 years, whom she met when he was a technical director at the National Theatre of the Deaf, survivors include two sons, Reuben Steinberg of Los Angeles and Joshua Steinberg of Temple City; four brothers; four sisters; and a grandson.

Ms. Frelich was the first deaf member to serve on the board of directors of the Screen Actors Guild and was an outspoken advocate for the rights of deaf actors.

“My goal is to have opportunities in theater for deaf people, the same as for other minorities,” she told the Reading (Pa.) Eagle newspaper in 1991. “We are a cultural minority. We feel we are different by language, not by physical disability.”