German-born American architect known for his postmodern steel-and-glass structures.

After graduating from the Technische Hochschule in Munich in 1965, Jahn moved to Chicago to study at the Illinois Institute of Technology, a school long associated with the Modernist aesthetic of Ludwig Mies van der Rohe (Mies van der Rohe, Ludwig) and his followers. On the basis of this solid design background, Jahn was hired by Chicago architectural firm C.F. Murphy Associates to work on the Miesian design for McCormick Place (1968–71) in Chicago. The firm was later renamed Murphy/Jahn, with Jahn becoming its president and CEO in 1983.

In the late 1970s and '80s, Jahn made his mark, designing extravagant buildings that combined historical and contextual references—the central tenets of postmodern architecture—with high-tech engineering solutions. The most notable, and at times controversial, example from this period is his State of Illinois Center (1979–85) in Chicago. Its plan refers to the American tradition of centrally planned domed state capitols. At the same time, its dramatic blue-and-pink glass-and-steel appearance and spectacular (if noisy and impossible to climatize) central atrium makes a bold, modern statement about the open nature of government. Jahn created other notable buildings in Chicago, including the steel-and-glass arched roofs of the United Airlines Terminal at O'Hare International Airport (1983–87). This shed is evocative of the grand Victorian railroad stations of the 19th century, while it also utilizes whimsical light and sound effects. His projects in the late 1980s and '90s included a series of international skyscrapers, such as Two Liberty Place (1989–91) in Philadelphia and several international Hyatt hotels.

By the turn of the 21st century, Jahn's buildings were beginning to sprout all over the United States and, indeed, the world. Notable later examples include the Munich Airport Center (1990–99), the Twenty-First-Century Tower in Shanghai (1999–2001), and the SONY Center in Berlin (1993–2000). In these later works, Jahn moved away from whimsy, a quality sometimes criticized in his early work, and instead adopted a more understated vocabulary rooted in European Modernism and straightforward engineering solutions.