He began his career at Crewe Alexandra, making his senior debut in April 2013, shortly after finishing a loan spell at Stafford Rangers.

Born in Market Drayton, Shropshire, Garratt graduated through the Academy at Crewe Alexandra to sign a 2+1⁄2-year professional contract in January 2013; manager Steve Davis noted that "we haven't had a goalkeeper to get excited about for a while".

[2][5][6] He made his senior debut for Crewe on 27 April 2013, in a League One tie against Walsall, two days after his 19th birthday, in a starting 11 comprised completely of Academy graduates; he kept a clean sheet in a 2–0 victory at Gresty Road.

[7][8] He faced competition from Steve Phillips and Alan Martin during the 2013–14 season and featured 27 times before he signed a new two-year deal with Crewe in May 2014; he was also named as 'Breakthrough Player of the Year' at the club's annual awards.

[24][25] Garratt won caps for England at under-17, under-18 and under-19 level, and was selected by head coach John Peacock for the 2011 UEFA European Under-17 Championship and 2011 FIFA U-17 World Cup squads.