But in 2005 something changed.
Lewis started composing large-scale musical works. His first was an eight-movement piece for Chicago's Joffrey Ballet. His latest work is a tribute to Abraham Lincoln - "Proclamation of Hope: A Symphonic Poem by Ramsey Lewis." It airs nationally on PBS stations starting Thursday.
It wasn't a smooth transition, Lewis said, until he stopped thinking in terms of the great composers he learned in his youth.
"I threw away the thought of Tchaikovsky and others and sat at the piano and started improvising," said Lewis, sitting in his downtown Chicago apartment, his piano nearby.
The result was immersive, he said.
"I did get off into the other world, if you get my drift, and I was able to compose from my spirit rather than from my intellect," he said.
Lewis, who has three Grammys and seven gold records, often performs in trios and is revered in jazz circles for his 1960s hits like "The In Crowd," "Hang on Sloopy" and "Wade in the Water."
Arranger, orchestrator and conductor Scott Hall has worked closely with Lewis, reviewing computer files of Lewis' handwritten compositions.
"I was just astounded by what was coming out of his head, through his fingers," said Hall, director of jazz studies at Columbia College in Chicago. "I had no idea he had this potential as a composer. Most people relate to him as the light side of the jazz world, and that's just not true."
That depth is obvious when Lewis, 76, describes how he approached composing the Lincoln work, which runs about 90 minutes. He went to Springfield and visited Lincoln sites, researched at the Chicago History Museum and amassed books and books of notes.
"I just immersed myself in all things Lincoln to the point where in my mind I had almost a running film of his life," Lewis said.
He chose eight sections of Lincoln's life and transformed each one into music. It took him nine months to complete.
"I wrote as if I was sitting in front of a screen and these moments recalled from my readings and research would go through my mind and they would send me off into a certain feeling, a certain mood," Lewis said. "At that point I left the universe, I left the spirit, I let all there was take over."
The work celebrates the 200th anniversary of Lincoln's birth. It debuted at the Ravinia Festival in June 2009 and was performed in November at the Kennedy Center in Washington. The PBS special features that performance.
Lewis' compositions reflect his classical music training, his gospel background and his life as a jazz musician, Hall said.
"He's very talented at taking a mood, whatever that mood may be or wants it to be, and putting it to music," Hall said. "There's a lot of music in his head that people weren't aware of all these years."
Those compositions add another layer to Lewis' musicianship, Hall said.
"It's just another stage in his life that is definitely going to enable him to continue his legacy," Hall said.
For Lewis, the combination of composing and performing has taught him life isn't just one moment that can be recaptured.
"Life is a solo, and it continues," he said. "I just know that when I put my hands on the piano it's going to flow."