Tomomi Hayashi studied architecture at Yokohama National University in Japan and Virginia Tech in USA. After graduation, he worked briefly for Maki and Associates in Tokyo and Rafael Viñoly Architects in New York. In cooperation with Siiri Vallner and Indrek Peil, he established the architecture office Head Arhitektid in 2001. In 2003, he worked with architecture office Kosmos and in the following year joined Coo Arhitektid that later grew into HGA (Hayashi Grossschmidt Arhitektuur). HGA was involved with the Estonian National Museum project from 2008 till it's completion as the collaborating local architects.
Since 2012 he has worked at the Architecture Institute of Tallinn University of Applied Sciences, since 2016 as an associate professor. He was nominated for the Mies van der Rohe Prize in 2005, 2009 and 2019.