The John L. O'Brien is one of six government buildings envisioned in the 1911 Capitol Master Plan. Construction began in 1938 and was completed in 1940. While built with reinforced concrete, the exterior walls feature broad expanses of unadorned sandstone. Pediment porticoes accent the north and west facades helping to align with the architectural design of the Capitol Group. The building was added to the National Register of Historic Places in June of 1979. It is the architectural companion to the Cherberg Building, with a public plaza located between them and the Legislative Building, following the original Capitol Campus Plan by Wilder and White.
Designed by architect Joseph Wohleb and originally called the "Transportation Building," this 100,700 square foot building is four-stories with a full daylight basement. It exhibits a bold Neo-Classical Revival composition with strong interior Art Deco design influences. The building was constructed with funding from the federal Project Works Administration and originally housed the state Highways Department and other agencies. In 1962, interiors were remodeled, occupancy changed and it was renamed the "Public Health Building." It was significantly remodeled a second time in 1970, to serve as offices for the House of Representatives. It was renamed in 1989 in honor of John L. O'Brien, speaker of the House from 1955 to 1963, longer than anyone else in state history.
A nearly $50 million rehabilitation of the building was completed in 2014. The multi-phase project overhauled the mechanical, electrical and plumbing systems, corrected life-safety code deficiencies, strengthened seismic resistance and realigned offices to improve space use of the upper three floors.
The upgrades and improvements were discreetly woven into the fabric of the 73-year-old building in ways that avoided or minimized impacts to historic walls or finishes.