Provided is a manufacturing method for a glass panel unit, with which it is possible to efficiently manufacture a glass panel unit having a desired dimensional shape. A first glass substrate (1) and a second glass substrate (2) arranged so as to face each other with a seal member (3) interposed therebetween are joined to each other with the seal member (3) therebetween. A glass panel unit is then manufactured by cutting, along a cutting surface (900) passing through the seal member (3), the first glass substrate (1), the seal member (3), and the second glass substrate (2) all at once starting from one side among the joined first glass substrate (1) and second glass substrate (2). A heat-insulating internal space (4) is preferably formed between the first glass substrate (1) and the second glass substrate (2).