Denis Arndt, a former helicopter pilot whose acting career reached its zenith when he made his Broadway debut at age 77 in the comedy “Heisenberg” and earned a Tony Award nomination, died on March 25 at his home in Ashland, Ore. He was 86.

His wife, Magee Downey, confirmed the death. She said the specific cause was not known.

Mr. Arndt built his reputation as a stage actor at the Oregon Shakespeare Festival in the 1970s and ’80s. He later became a familiar face on television series like “L.A. Law” and “Picket Fences” and played one of the detectives who interrogate Sharon Stone in a famous erotically charged scene in “Basic Instinct” (1992).

He first appeared in “Heisenberg,” a two-character play by Simon Stephens, which the Manhattan Theater Club produced at City Center’s Studio at Stage II in 2015. The play transferred to the Samuel J. Friedman Theater on Broadway the next year.

Mr. Arndt played Alex, a reserved, 75-year-old Irish-born butcher, who is in a London train station when he is unexpectedly kissed on the neck by Georgie (Mary-Louise Parker), a loud, impulsive and mysterious 42-year-old American. Her boldness ignites a romance.

Ben Brantley, reviewing “Heisenberg” in The New York Times, called Mr. Arndt and Ms. Parker “the sexiest couple on a New York stage now.” Mr. Arndt, he wrote, “makes what has to be the most unlikely and irresistible Broadway debut of the year. He lends roiling, at first barely detectable energy to the seeming passivity of a man who, on occasion, finds himself crying for reasons he cannot (nor wants to) explain. But this ostensibly confirmed celibate oozes a gentle, undeniable sensuality.”

In an interview with The Times during the run of the play, Mr. Arndt spoke ecstatically about the chemistry he felt onstage with Ms. Parker, who was appearing in her seventh Broadway show.

“I feel compelled to give her my complete attention,” he said. “I see the goddess. I do. I truly do.”

Mr. Arndt, Ms. Parker told The Times, “is everything I could want — passionate and so smart and so sensitive.”

The Heisenberg of the play’s title is the Nobel Prize-winning German physicist Werner Heisenberg, known for his uncertainty principle. That principle is not mentioned by the characters, but his name evokes the unpredictability of their romance.

Mr. Arndt was nominated for the Tony for best actor in a play in 2017 but lost to Kevin Kline, who won for his performance in the Noël Coward comedy “Present Laughter.”

When Mr. Arndt and Ms. Parker reprised their roles at the Mark Taper Forum in Los Angeles in 2017, Charles McNulty of The Los Angeles Times wrote, “Arndt lends poignant majesty to his character’s rediscovered sensuality.”

Denis Leroy Arndt was born on Feb. 23, 1939, in, Clyde, Ohio, and later moved with his parents and two younger sisters to Spokane, Wash. His father, Bryce, was a railroad switchman, and his mother, Arline, owned a seamstress shop, where she made curtains.

He started acting in high school, but after graduating he enlisted in the Army, where he spent about a decade. He trained as a helicopter pilot and later flew missions in Vietnam, receiving two Purple Hearts when his aircraft came under fire. He enjoyed flying — “You had the machine in your hand, and it became an extension of your central nervous system,” he told The Times — and worked as a commercial pilot in Alaska after his discharge.

He studied history at the University of Washington on the G.I. Bill, but he did not graduate and soon began acting in Seattle theaters. In the 1970s, he started a long association with the Oregon Shakespeare Festival, in Ashland.

Mark Murphey, who shared the stage with Mr. Arndt in “Hamlet,” “Romeo and Juliet” and “Two Gentlemen of Verona,” said in an interview: “As an actor, he was in the moment; he was different every time, every night was different. He was just incredibly vital and riveting. He just had that edge.”

Mr. Arndt played the lead in “King Lear,” Eugene O’Neill’s “Long Day’s Journey Into Night” and other plays at the festival and often performed at other theaters on the West Coast. He also appeared in Michael Weller’s “The Ballad of Soapy Smith” at the Public Theater in Manhattan in 1984 and “Richard II” at the Delacorte Theater in Central Park in 1987.

In 1988, he left the Oregon festival, where he was playing Hickey in O’Neill’s “The Iceman Cometh,” to join the cast of “Annie McGuire,” a new sitcom starring Mary Tyler Moore, as her husband, a construction engineer. He had already done some film and television work, but a commitment to a series with a star like Ms. Moore was something new in his career.

The Sunday Oregonian newspaper reported at the time that some people at the festival were upset that Mr. Arndt had left. But, he told the newspaper, landing a role in a high-profile network series was a reward for his years of stage work. “The idea of being invited to play marbles with the big kids is something we all aspire to,” he said.

(He would return to the Oregon festival in 2014 as Prospero in “The Tempest” and in multiple roles in “The Great Society,” the second of Robert Schenkkan’s plays about President Lyndon B. Johnson.)

“Annie McGuire” lasted only 10 episodes, but Mr. Arndt soon became a regular presence on television. He played lawyers in recurring roles on “L.A. Law,” “Picket Fences” and “The Practice” and was seen on “Boston Legal,” “Life Goes On,” “Supernatural,” “Grey’s Anatomy,” “The Good Fight,” “How to Get Away With Murder” and “Mr. Mercedes.”

In addition to his wife, Mr. Arndt is survived by two daughters, McKenna Rowe and Bryce Brooks, and a son, Tanner Arndt, from their marriage; three daughters, Tammy, Laurie and Kirsten Arndt, and a son, Scott, from his marriage to Marjorie Arveson, which ended in divorce; and many grandchildren, great-grandchildren and great-great-grandchildren.

Mr. Arndt was not the first choice for “Heisenberg,” but he stepped in quickly when Kenneth Welsh, who was originally cast in the Off Broadway production, left four days before rehearsals were to begin.

“I was prepared for this,” Mr. Arndt told The Los Angeles Times. He added, “My insight, chemistry, with this woman, her incredible skill — it’s too much fun to use all the tools in my box.”