Planning for a new student union began more than ten years before it became a reality. The proposal for a new union was first made public in December 1955. A "State of the Union " series of Polytechnic articles informed the student body about the history of the Rensselaer Union, the state of inadequate and overcrowded spaces in the Club House and the need for a center for student life on campus. In March 1958, a referendum was presented to the student body to increase the student activity fee by $5 to fund a student union. The referendum was voted on during the Grand Marshal election in April and passed with 79% of students supporting the measure. A survey gathered student feedback as to what features they wanted to see in a new union. Though the building was expected to be completed before the Class of 1961 graduated, another six classes would leave Rensselaer without seeing a new student union.

Ernest J. Kump Associates was chosen to design the $3 million building and construction began in early 1965. Students contributed more than $250,000 towards the cost. The Union , placed on the 15th Street campus corridor, was designed to be a true center of student activity with recreation areas, a snack bar, bookstore, meeting rooms, offices for student organizations and student services, etc. A strike during the summer of 1965 delayed the construction of the Union as well as the completion of housing projects on campus. The new Rensselaer Union was finally opened to students in May 1967 and the building was formally dedicated in October. The main dining hall was named the McNeil Room in honor of Frank McNeil, director of the Union from 1929 to 1968.

In 1983, students passed a referendum for an addition to the Union to expand the bookstore. A one-story addition was approved by the Board of Trustees in 1985. The bookstore expanded on the southwest side and added storage space on the south side.