The promising Shropshire-born goalkeeper joined Shrewsbury direct from school and quickly found himself elevated to the international stage by earning England youth honours.
He made his debut for the England under-16s in a 1-0 win over Spain in Madrid and has since been capped at under-17 and under-18 level.
Callum was loaned out to both Market Drayton and Workington early in the 2013-14 season to aid his development ahead of signing his first professional contract at the Greenhous Meadow in March 2014.
Callum enjoyed impressive displays against both West Bromwich Albion and Watford in friendlies leading up to the start of the 2014-15 season.
After a number of appearances on the Town bench, Callum finally made his league debut against Swindon Town on the final day of the 2015-16 season.
Callum went onto sign a new two year deal just a few weeks later to keep him at the club until the summer of 2018.