Portage III was constructed between 1973 and 1978 at a cost of $88 million dollars. Set in a line along the riverfront, giving the complex it's distinctive skyline from the Ottawa side, the facility consists of six towers, a commercial area, two basement levels, and a tri-level underground parking garage (known as the Laurier-Taché Garage) that may accommodate 1,676 vehicles and 48 handicapped parking spaces. The towers are grouped into three cores, which are linked by a three-story bridge over Maisonneuve Boulevard (referred to as Towers D and E). Tower A has fifteen and eighteen floors, Tower B has ten and twelve floors, Tower C has nine and twelve floors and Tower D and E have two and three floors respectively. The office area totals106,434 square metres and the parking garage and storage areas totals 42,907 square metres. The commercial area is occupied by nine (9) retail tenants. The number of building occupants is estimated at 4,500.

Place d'Accueil (an area totaling 4,310 square metres) is the focal point of the pedestrian and vehicular systems, it serves as the facility's bus terminal and is located on the east and west side of Maisonneuve Boulevard. Place Aubry, located between Portage III and IV, consists of a hard surfaced landscaped park leading to Promenade du Portage. Both of the latter areas form part of Portage III.

Portage III is considered to be, as noted in its 2002 Asset Management Plan, an upgraded older building with a high occupancy rate in a prime location. It is viewed to be a Class B+ building and serves as the headquarters for Public Works and Government Services Canada (PWGSC). It is the principal tenant.

A major space optimization project ongoing since 1991/1992 was completed in 1999/2000. PWGSC is currently consolidating its operations in Portage III by gradually moving staff from other National Capital Area buildings into optimized office space.

In September 1996, PWGSC entered into an energy savings contract with MCW through a process of request for proposals. The contract has a duration extending 8 years beyond February 1998. In essence, MCW provides engineering, project management services and funding for the project, while PWGSC progressively reimburses their capital investment from the savings realized. The lighting retrofit portion was completed in March 1997 and mechanical upgrades were completed in October 2000. In March 2002, all the toilets (a total of 300) were replaced by MCW in collaboration with the contract, water savings are expected.

IIn 1999/2000, PWGSC began Part 1 of the rehabilitation of the 25 year-old Laurier-Taché Garage. This multi-year, $ 43 million dollar project was done in concert with the construction of the Hull portion of the Confederation Boulevard (managed by the National Capital Commission). Part II of the project started in Spring- 2004. The third phase recently started and consist of the interior slab replacement, closure of 600 parking stalls for each sectionclosure of the daily parking stalls (350) in order to accommodate monthly federal and commercial tenants during the construction. This project was completed in 2008.

In 1999/2000 the tower A and B lobby, located on level 0, were upgraded as part of PWGSC's celebration of the Millennium. Tower C lobby was upgraded in March 2002. The new ceiling and lighting improved immensely the appearance.

The Food Court located on commercial level between Tower B and C was totally renovated in July 2001. This provided a more accessible, as well as a more inviting environment, for all occupants. The new Food Court is smoke-free and very popular. The area is maintained by SNC-LAVALIN Profac in-house personnel.