"While there are sure to be other Mansfield letters out there, we are certain this is the last big clump."
Mr Colquhoun said a display would be made early this week in the library's newly reopened reading room with the rest of the material open to researchers by October.
Digitising the material would also be undertaken for the benefit of Mansfield's large international following.
Katherine Mansfield Birthplace director Mary Morris said the arrival of the new material at Alexander Turnbull Library was hugely exciting.
"It's absolutely amazing. Some of these letters and items may shed light on aspects of her life that we don't know much about.
"The letters give us her world, the context she was living in and having that helps our understanding of who she was and that is significant for the Katherine Mansfield Birthplace.
"She has a particular place in New Zealand's cultural history and heritage and the more we can know about her the better."
Ms Morris said the Birthplace had a long-standing relationship with the Alexander Turnbull Library. Whether some of the items made their way into the Tinakori Rd house depended on future programming.