Starting his career at Cambridge United, John made 39 league appearances before signing for Premier League Everton in the summer of 2005, following a successful trial.
He then had loan spells with Walsall, Rushden & Diamonds and Chester City before making his bow for the Toffees against Blackburn Rovers in February 2006.
He spent further spells out on loan at Stockport County, Wrexham, Bristol City and Crewe, prior to spending the 2009/10 season at Scottish Premier League side Motherwell, keeping 15 clean sheets from 34 appearances.
That July he joined Championship club Norwich City on a permanent deal and went on to make 235 league appearances in seven years at the club. During his time at Carrow Road he twice won promotion to the Premier League and spent four seasons playing in the top flight with the Canaries.
He moved to Wolverhampton Wanderers in July 2017 and was a key performer as the club won promotion to the Premier League in his first season.
While John was unfortunate to miss out on Euro 2012 due to a broken finger, his England debut came against Italy that August, making a number of key saves in a 2-1 victory for the Three Lions.