The companies have worked collaboratively on projects for more than 10 years.
Partners from 20 Below, an eight-person architectural and design firm based at 23 4th St. NE, will join Architectural Alliance's leadership team, according to a news release about the merger.
Architectural Alliance, based in Loring Park, was founded in 1970 and has been experiencing significant growth in recent years.
"Together, we will offer greater reach, creativity and experience in the architecture and design market," said Carey Brendalen, a principal at Architectural Alliance. "... Quite simply, the combined firms will allow us to build even stronger teams. Our unified energy, effort and commitment will generate new and unique perspectives for solving client problems."
Heather Rose-Dunning, a 20 Below principal, added: "Our combined attitude and outlook for the future means we will be able to do even more for our clients."
A local project of note for 20 Below is the new American Academy of Neurology Headquarters in the Mill District. Architectural Alliance has been involved in several high profile local projects, including the Guthrie Theater, buildings on the University of Minnesota campus and the Central Library.