“That was ‘Memory,’ by Webber and Rice and Puccini and Ravel,” Mr. Nero would tell the audience, offering a characteristically mischievous explanation from the podium. Once, describing his improvisatory version of Jerome Kern’s “All the Things You Are,” he noted that the song was “semi-jazz and quasi-Bach.”

Mr. Nero, who died July 6 at 89, was among the country’s most beloved pops conductors, known for applying a classical framework to popular music or, working in the opposite direction, for incorporating popular melodies and jazz techniques into classical works. He led the Philly Pops orchestra for more than three decades, at times playing the piano with his right hand while conducting with his left, and was also comfortable at smaller venues, pushing and prodding at musical boundaries while playing at nightclubs, lounges and White House state dinners.

“In a normal concert, I’ll run the gamut from heavy classics to heavy pops; I don’t put things in categories,” he told The Washington Post in 1988. “My message to the audience is that music is music.”

Mr. Nero recorded dozens of albums, performed on “The Tonight Show Starring Johnny Carson,” and appeared with singers including Frank Sinatra, Johnny Mathis, Mel Tormé, Rod Stewart and Ray Charles. Some critics scorned his easy-listening albums, dismissing the quality of his material, although he won two Grammy Awards and was unabashed in calling himself “MOR: ‘middle of the road,’ and doing great business.”

A piano prodigy who started taking lessons when he was 7, he began performing Haydn concertos from memory at age 11 and had his television breakthrough the year he turned 18, when he was invited to appear in a 1952 television special, playing piano as Paul Whiteman conducted an orchestra in a rendition of Gershwin’s “Rhapsody in Blue.”

Within a few years, Mr. Nero had turned to jazz, inspired by recordings of pianist Art Tatum. But he struggled to develop his own sound — while playing at clubs in New York, “every night was torture,” he told High Fidelity magazine — until he discovered that he could apply the structures of classical music to contemporary pop tunes. In 1960, he signed a record deal with RCA, leading to some two-dozen albums in eight years.

His first, “Piano Forte” (1961), included instrumental versions of “Over the Rainbow” and “My Funny Valentine.” “There must have been twelve tunes with eight different approaches,” he told the Daily Oklahoman decades later. “One was Mozartean, the next one was in the style of Rachmaninoff, the next was a straight ballad and another was a jazz approach. The idea was to see what came out of this and the response was that everybody liked something different. In other words, the material dictates the approach.”

Mr. Nero won a Grammy Award for best new artist of 1961. He was later honored for his 1962 album “The Colorful Peter Nero” and received eight Grammy nominations altogether, including for his recording of the theme for the coming-of-age film “Summer of ’42” (1971), by French composer Michel Legrand. Mr. Nero’s single, and a 1972 album of the same name, each sold more than 1 million copies.

By then he had started to branch into composing and conducting. Mr. Nero wrote the score to the 1963 romantic comedy “Sunday in New York,” starring Cliff Robertson, Jane Fonda and Rod Taylor, and made a cameo in the film, performing at a fictional venue appropriately dubbed “Club Nero.” In 1970, he premiered an orchestral and choral piece based on Anne Frank’s posthumously published “The Diary of a Young Girl,” which chronicled the two years she spent living in hiding during the Holocaust, before being sent to her death at a Nazi concentration camp.

Mr. Nero was reportedly the first person to give the work a musical setting, and said he got permission to adapt the book from Frank’s father, Otto, an Auschwitz survivor who was then living in Switzerland. Written over 10 months, the work premiered at a synagogue near Mr. Nero’s home on Long Island, and received its first full-scale production three years later in Trenton, N.J., where he conducted a full symphony and more than 100 singers, plus several jazz musicians.

Early performances featured his two adolescent children: Beverly, who sang and narrated, and Jedd, who played the drums.

“He really just poured his life into the writing of it. He must have channeled her,” Beverly Nero said in a phone interview. “He knew this was something for everybody. You can feel the pain and the joy of the 14-year-old in the love songs, of just discovering love for the first time in the attic. My dad was a romanticist — all of the romance is in there, all of the family life.”

Mr. Nero conducted and played piano in the work, and went on to work as a conductor with orchestras across the country, including while helming pops concerts for the Florida Philharmonic Orchestra in Fort Lauderdale and the Tulsa Philharmonic in Oklahoma.

He joined the Philly Pops in 1979, when it was founded by theater impresario Moe Septee, and remained for 34 years until leaving in 2013, after the Pops said it could no longer afford to pay his reported $500,000 annual salary. (The organization has an uncertain future, and was evicted from its longtime home, the Kimmel Center in Philadelphia, earlier this year.)

As a conductor, he “somehow manages to be both erudite and haimish, with a little showbiz humor thrown in for good measure,” Philadelphia Inquirer music critic Peter Dobrin wrote in 2012, after Mr. Nero unveiled a Christmas version of the South Korean pop hit “Gangnam Style.”

Mr. Nero preferred to play concerts without a program, taking his cue from audience reactions. He made exceptions for symphony orchestras but still sought to maintain a certain freedom. “When I’ve had a chance to gauge the kind of audience I have and decide what direction I should take,” he told the New York Times, “I revise the printed program after the first number, tear it apart.”

The older of two sons, Mr. Nero was born Bernard Nierow in Brooklyn on May 22, 1934. His father, a Jewish immigrant from Eastern Europe, directed the Pride of Judea Children’s Home in Brooklyn and served as a deputy commissioner of the New York City Youth Board. His mother, the daughter of Jewish immigrants from the Greek island of Rhodes, taught Spanish at a local high school.

Neither parent was musical, but after Mr. Nero began banging out songs on a toy xylophone they encouraged his interest in music, arranging to buy a used Steinway piano for $1,100 — almost $19,000 in today’s money. “It was the only time they borrowed money,” Mr. Nero said.

While studying at the High School of Music & Art, a magnet school in Manhattan, he earned a scholarship to take classes part-time at the Juilliard School. He later took private lessons with pianist Constance Keene, and in 1956 he received a bachelor’s degree in music from Brooklyn College.

As he launched his performing career, Mr. Nero dropped the “w” from his last name and then cut the “i,” and followed his manager’s suggestion in going by Peter instead of Bernie. “If I had to do it again, I would never change my name,” he told an audience in 1998, giving a lecture in the Philadelphia suburbs.

Mr. Nero’s two children were from his first marriage, to Marcia Dunner, which ended in divorce. His subsequent marriages to Peggy Altman and Rebecca Edie, a Philly Pops pianist, also ended in divorce.

Mr. Nero lived in the Villages, Fla., until about six months ago, when he moved to an assisted-living center in nearby Eustis, where he died. His daughter, Beverly, did not know the exact cause but said he had arthritis and was receiving hospice care. In addition to his daughter, survivors include his son; his brother; and three grandchildren.

While hand and back pain prevented Mr. Nero from working in recent years, his daughter recalled that when she and her brother were growing up, Mr. Nero practiced “every single day, for hours and hours,” even as he pursued interests outside music. He dabbled in computer programming, kept up with the latest technological advances (he was an early proponent of the cellphone and video phone, and appeared in advertisements for Radio Shack) and showed an unusual talent for multitasking.

“He would play on a silent electric keyboard with one hand,” his daughter said, “while doing the New York Times crossword with the other hand, in pen.” At night, he would continue to practice even as he watched “The Tonight Show” on a miniature television set, listening through headphones to avoid bothering the rest of the family.

“He would just be sitting there laughing at Johnny Carson’s monologue,” his daughter said, “but his hands were flying” on the keyboard.