With many one-person and group exhibitions, he has shown his abstract paintings regionally, nationally, and abroad. In 1988, his work was the focus of a 20-year survey exhibition at Linda Durham Gallery in Santa Fe.[1][4] His work from the last forty-five year was the subject of a retrospective exhibition in 2013 at American University's Katzen Arts Center in Washington, D.C., and Goya Contemporary in Baltimore.
He is a recipient of a NEA fellowship in painting, as well as an individual artist's grant from the Maryland State Arts Council.
He has taught at Pomona College in California, the University of New Mexico in Albuquerque, and since 1990 at Maryland Institute College of Art (MICA).[2] Twice he has received the Trustee's Award for Excellence in Teaching at MICA, and has been nominated for the Richard C. Diebenkorn Teaching Fellowship. In addition to teaching and painting, he has written on the work of other artists, lectured on his own work, and curated exhibitions of abstract painting.
2009, The Grey Zone: Abstraction and/or Representation Paintings and Drawings by Timothy App and Howie Lee Weiss, Howard Community College, Columbia, Maryland, U.S.