[6] Sebastian has signed a one-year partnership contract with the Glasgow Warriors which ran until May 2016.
It was a full-time professional contract that allowed Sebastian to play for Ayr RFC when not on Warriors duty.
[9] In June 2021, Sebastian was called up to the Scotland squad for the summer internationals against England A, Romania and Georgia.
He won his first cap by coming on as a second half substitute during the Autumn Internationals in a match against Japan on the 20th Nov 2021.
[11] In 2023 Sebastian was selected in Scotland's 33 player squad for the 2023 Rugby World Cup in France.