The modern station with both subway and commuter rail levels was designed by Cambridge Seven Associates and opened on December 8, 1984.

Passenger trains from the Lexington Branch and the Central Massachusetts Railroad were diverted to the Fitchburg mainline and began to stop at Cambridge station.

[10] In 1937–38, the Boston and Maine Railroad built a two-story brick depot by the bridge, with the ticket office at street level and the waiting room and platforms below.

[13] By the time the newly formed Massachusetts Bay Transportation Authority (MBTA) began subsidizing northside commuter rail operations in the late 1960s, both the Lexington Branch and the Central Mass Branch had been reduced to single rush hour round trips on poorly maintained track.

[1] In the late 1970s, Cambridge station was renamed to Porter when it became certain that the Red Line Northwest Extension would include a stop there.

[15] A new glass and concrete headhouse was built around 1982, and the complete new transfer station opened on December 8, 1984, along with Davis.

It served this role during the 2004 Democratic National Convention, when North Station was closed for a week for security purposes, and during Green Line Extension construction in 2015 and 2019–20.

[1][19] Additional weekday short turn service was operated between Porter and North Station from July 15–26, 2024, providing half-hour headways between those points while the Red Line was closed for maintenance work.

The Fitchburg Line runs approximately east-west in an open cut, with a single island platform between the two tracks.

It contains fare machines, faregates for the Red Line, a convenience store, and – unusually for the MBTA system – public restrooms.

[5] Porter's unusual depth is due to the MBTA's decision to build the station in bedrock rather than soft clay, saving time and money in the construction process.

[26] Passengers reach Red Line platforms via a series of escalators, stairs totalling 199 steps, or a set of elevators.

[29] The elevator to the Red Line platforms was out of service for construction from March 21, 2011, to June 22, 2012; an accessible shuttle bus ran between Porter and Davis.

[24][29] The elevator to the commuter rail platform was also taken out of service from December 9, 2011, to July 2012; a shuttle bus ran between Harvard, Porter, and Waltham.