While at the University of Alabama he was befriended by the American football quarterback Joe Namath, met visiting artist Theodoros Stamos, and primarily studied painting with Melville Price, a painter who had shown in New York City with Franz Kline and Willem de Kooning and had been a member of The Club at the Cedar Tavern.

During these years, Willis also participated in the Civil Rights Movement including the march from Selma to Montgomery, led by Martin Luther King Jr.

In New York, Willis met fellow painters, Dan Christensen, Jules Olitski, Ken Showell as well as sculptors and installation artists Richard Serra, Alan Saret, and Gordon Matta-Clark, all working out of a process art orientation.

Some of the other artists connected with Lyrical Abstraction were Victoria Barr, Jake Berthot, Dan Christensen, Ronnie Landfield, Pat Lipsky, John Torreano, Phillip Wofford and Robert Zakanitch.

The “Slat” series also attracted Bykert Gallery director, Klaus Kertess, and in 1971 Willis joined the Paley and Lowe Gallery, New York City, as part of its original stable of eight artists including, Joan Snyder, Mary Heilmann, Peter Pinchbeck, Herbert Schiffrin, Fred Gudziet, Mike Bakaty, Peter Bradley, and Michael Goldberg who joined later.

In 1979, Thornton Willis exhibited his “Wedge” Paintings at the 55 Mercer Street Gallery where the work attracted the attention of British collectors, Robin Symes, and Charles and Doris Saatchi.

He showed the “Wedge” paintings at the Sidney Janis Gallery, NYC, in 1980 is an exhibition entitled “Seven Young Americans” curated by Sam Hunter which included friend and fellow artist Sean Scully.

“Striped Suit”, 1982, a large double wedge canvas was featured on the cover of Arts Magazine with an essay by Steven Henry Madoff, Looking for Thornton Willis: A Treatise.

A one-person exhibition of large scale Triangle paintings and oil stick on paper followed in 1993, at the Andre Zarre Gallery [11] where the artist employed a tight grid overridden by gesture and a plastic color palette.

In the 2001 catalogue essay for Painted in New York City: The Presence of the Past, art critic Robert C. Morgan noted Willis's Abstract Expressionist roots and the newer element of restraint.

Combining the early "Slat" paintings, with exploration of form and field in his “Wedge” series, he created a body of work he entitled “Lattices” where lines appear to weave forward and back.

Michael Feldman documented the transition to this new work in a film, in 2008-09, Portrait of an American Painter [17] In 2009, Willis had a one-person show at the Elizabeth Harris Gallery, with catalog entitled The Lattice Paintings essay, by James Panero[18] of The New Criterion.