Born and raised in the small town of Simpele located near the Russian border, Joronen joined Fulham Academy in 2009. In June 2010, Joronen signed his first professional contract with the club, which will keep him until 2013. In May 2012, Joronen signed a two-year extension with Fulham, that will keep him until 2014. Six month later, on 25 October 2012, Joronen joined Maidenhead Unitedon loan and in February 2013, Joronen was loaned to Cambridge United. Only a day later Joronen returned to Fulham after he refused to be named as a substitute for Cambridge. After a loan spell at Maidenhead United, Joronen then move back to Finland, where he joined Veikkausliiga side FC Lahti on loan until August. After making eighteen appearance for the club, which he established himself as a first choice goalkeeper, Joronen returned to his parent club in early August. At the start of the 2014–15 season, Joronen signed a two-year contract with the club that kept him until 2016. He was then given his debut as the starting goalkeeper in Fulham's opening game in the Championship against Ipswich Town on 9 August 2014. After making three more appearance for the club, Joronen soon lost his first team place to Marcus Bettinelli and new goalkeeper signing, Gábor Király. Joronen joined Accrington Stanley on loan for one month on 17 October 2014. Shortly after, he made his Accrington Stanley debut the next day, on 18 October 2014, starting in goal, in a 2–1 loss against Stevenage. However, after making three more appearance at Accrington Stanley whilst on loan, he returned early after dislocating his kneecap during a League Two match against Morecambe. Then, it was announced that Joronen would be out for three to four months. On 27 August 2015, Joronen signed for Stevenage on loan until January 2016. He made his Stevenage debut two days later, in a 1–1 draw against Dagenham & Redbridge. Joronen scored with a long-range clearance in a match against Wycombe Wanderers on 17 October 2015. He then kept his first clean sheet in a 3–0 win over Gillingham in the first round of the FA Cup. However, after making eleven appearance for the side, Joronen suffered an injury during the match against Gillingham and subsequently returned to his parent club. After returning to his parent club, Joronen signed a contract extension, keeping him until 2017. In the 2016–17 season, Joronen was featured three times in the EFL Cup, being the first choice goalkeeper ahead of Bettinelli. At the end of the 2016–17 season, he was offered a new contract by the club.
However, instead of signing a new contract and pursue to leave the club over first team football, Joronen left Fulham to join Danish side AC Horsens, signing a two-year contract on 10 July 2017. Joronen made his AC Horsens debut in the opening game of the season, in a 2–1 win over AGF Aarhus. On 4 August 2017, he kept his first clean sheet for the side, in a 1–0 win over Silkeborg, a win saw the club go at the top of the table.
On 15 December 2017, it was announced that Joronen will join Copenhagen in the summer of 2018 for a fee of €875,000. He has signed a five-year contract. He made his competitive debut on 23 July 2018, playing the entirety of a 3–0 league victory over Hobro.
International career
Having represented Finland at U17, U19 and U21 level, Joronen was called up to the senior squad and made his debut for Finland in the 2013 King's Cup against Thailand on 24 January 2013.
