Krul's career began at youth clubs RAS and ADO Den Haag before moving to Newcastle United in 2005.

His career continued at Norwich City, where he was named the club's Player of the Season and won the EFL Championship twice.

He joined Premier League club Newcastle United in the summer of 2005 on a three-year deal after failing to sign professional terms.

[4] Following an injury to Newcastle's first-choice goalkeeper Shay Given, Krul appeared on the bench as back-up to second-choice Steve Harper.

His debut was well-received; he displayed his shot-stopping abilities, saving efforts from Giuseppe Biava and David Di Michele and recording a clean sheet in the process.

[citation needed] On 3 August 2007, Krul joined Scottish side Falkirk on loan, originally until 1 January 2008 though it was later extended until the end of the season after a number of impressive performances.

[citation needed] On 21 November 2008, Krul joined Carlisle United on a one-month loan from Newcastle to replace Ben Alnwick, who had rejoined Tottenham Hotspur.

Krul started his first league game for Newcastle on 2 May 2010, the last day of the Championship campaign, against Queens Park Rangers at Loftus Road and kept a clean sheet.

[12] Krul made his Premier League debut for Newcastle on 18 September 2010 against Everton at Goodison Park, coming on as a substitute in the 35th minute for the injured Steve Harper in a match that ended in a 1–0 win for the Magpies.

[17] Although he received criticism from Arsenal player Jack Wilshere,[18] teammate James Perch defended Krul, believing van Persie "out of order".

[24] He injured his ankle during a Europa League match in the Round of 32 against Ukrainian side Metalist Kharkiv which ruled him out for five weeks.

[25] In the Tyne–Wear derby on 14 April 2013, Krul suffered a dislocated shoulder on 57th minutes after he landed awkwardly after punching away an Adam Johnson free-kick.

[30] Krul's performance was praised by Newcastle United goalkeeping legend Pavel Srníček[31] and manager Alan Pardew.

[34] On 25 August 2016, Krul signed a one-year contract extension at Newcastle United before joining Ajax on a season-long loan deal to provide him with top-tier first-team football as he continued his recovery from injury.

[36] On 31 August 2017, Krul signed for Premier League club Brighton & Hove Albion on a season-long loan, reuniting him with former Newcastle manager Chris Hughton.

[42] Krul was named Norwich City's Player of the Season in the club's 2019–20 campaign, making him only the fifth ever different goalkeeper to win the Barry Butler memorial trophy.

[43] He proceeded to miss a number of games between then and the end of January, with McGovern or Daniel Barden deputising, but eventually regained his place as Norwich won the Championship and promotion back to the Premier League.

[47] On 17 August 2023, Krul signed for newly promoted Premier League club Luton Town with an undisclosed contract length.

[citation needed] On 4 June 2011, Krul made the starting eleven for the Netherlands in a friendly against Brazil, his first cap at senior level.

In new coach Louis van Gaal's first competitive game in charge against Turkey in Amsterdam, Krul was selected as starting goalkeeper, keeping a clean sheet in a 2–0 win for the Oranje.