The school announced the purchase of the new site at 66 Stratton Rd on Thursday after swelling enrollment numbers meant the Catholic college had to expand.
"In a world that is both enabled and disrupted by technology, the opening of a second campus that allows our students to connect to the community and environment is both brave and necessary," St Joseph's College principal Michael Delaney said.
"This announcement continues the courageous journey of the Brigidine sisters who founded St Joseph's College.
"From the very beginning, our college story has been one of commitment and willingness the break new ground."
In the official announcement of the land purchase, Kildare Education Ministries Board chairperson Sister Louise Cleary said the school has stayed true to its roots.
"Since its establishment in 1886, St Joseph's College has been known as an inclusive school offering quality Catholic education appropriate of the times," she said.
"The new campus is an exciting educational venture that will enhance contemporary learning and provide for the growing number of students.
"The board is confident the master planning under way will lead to facilities and education provision on both campuses that will enrich St Joseph's as a Kildare Ministries school in the Brigidine tradition."
Mr Delaney said the commitment to the new site, which is 80 acres in size, now gives specific direction to the development of plans for future facilities.
The plan includes a multi-million dollar upgrade of the Dickson St facilities as well as the commissioning of a state of the art, sustainable and custom designed new campus; two complex projects that are hoped will come to fruition over the next six to eight years.
"We remain one Catholic learning community in the Brigidine tradition. Our two campuses, only 4km apart, will exist in harmony and balance, accessible and complementary, strong and kind: two siblings in a close relationship," Mr Delaney said.
Students from Years 7 to 9 are expected to to be moved onto the new campus while Years 10 to 12 will remain on the Dickson St campus.
More information can be found on the school website or by contacting the school's front office.