It serves as an intermediate stop for Amtrak's Cascades and Coast Starlight routes and, along with King Street Station in Seattle, is one of two western termini of the Empire Builder.

The station building contains Wilf's Restaurant & Bar on the ground level and offices on the upper floors.

It also has Amtrak's first Metropolitan Lounge on the West Coast,[3] which is reserved for first-class sleeping car and business-class passengers.

[4] Southeast of the station, the tracks make a sharp turn and cross the river on the historic Steel Bridge.

Located at the northern end of TriMet's transit mall, Union Station is also only a short walk to both lines of the Portland Streetcar, in the Pearl District.

It was built by the firm of Wakefield and Bridges for the Northern Pacific Terminal Company at a cost of $300,000 ($11 million in 2023 adjusted for inflation), and opened on February 14, 1896.

[10] The annex, also constructed in 1896 also by Wakefield and Bridges, contained the freestanding steam plant, storerooms, telegraph office, laundry, and police-room.

Passengers gained entry to the tracks by passing through along, narrow, enclosed one-story shed appended to the east side of the station.

[11] [12] The track shelters were built in response to the expected increase in travellers arriving by rail to attend the 1905 Lewis and Clark Exposition in Portland.

The Interlocking Tower at Union Station is believed to be the only remaining building of its type in Oregon, and one of just five in the western United States.

[13] This interlocking tower was added to the National Registry of Historic Places form for Portland Union Station in a 2015 update .

Dissatisfaction with the lack of a clear, formal entry and confusing circulation patterns and dramatically increased passenger load were factors that led to the need to remodel.

Major changes included: structural, functional and formal reordering of the main waiting room (including removing interior cast-iron columns) and associated public spaces; reorganizing the entry and exit sequences from the street and tracks; and functional and formal reorganization of the wing between the restaurant dining room and the main hall.

Expansion of service at Union Station related to the Spokane, Portland and Seattle Railway line in 1920s required significant changes to the building and track, and at its peak period of operation in the late 1940s Union Station had as many as 30 separate tracks, continuing east to Front Avenue.

[25] According to The Oregonian, talks to sell Union Station to Amtrak stalled in early 2024 and Prosper Portland was still seeking a buyer who would be able to finance seismic retrofitting and other upgrades that are estimated to cost $250 million.