His artwork is shown in galleries such as in London's Aquarium Gallery and New York's Clementine Gallery. both in 2006, and the 2008 Liverpool Biennial. Currently his work is being exhibited as "The Museum of Love" at Verge Gallery in Sacramento, California.
In 1993 Johnston was commissioned to paint a mural of the Hi, How Are You? frog (also known as "Jeremiah the Innocent") from his 1983 album cover on the side of the Sound Exchange record store located on the corner of 21st and Guadalupe in Austin, Texas (the "Drag"). At the time, the frog image had recently become nationally recognized from media images of Kurt Cobain wearing a "Hi, How Are You?" t-shirt during Nirvana's promotion of their 1991 album Nevermind. In 2004 locals successfully endeavored to preserve the image when the building changed ownership to a Baja Fresh restaurant and more recently to a sushi restaurant called Crave. In Spring 2008, a Jeremiah the Innocent collectible figurine was released in limited runs of four different colors.
As of June 2010, a biopic about Johnston's life featuring Gabriel Sunday of My Suicide is in production.