Since the 1990s, his status as a celebrity has mainly been fueled, not by his sporting achievements, but instead by his colourful personal relationships, his career as a singer, and various incidents often related to heavy use of alcohol and violent behavior. He was sentenced to jail for 26 months following a stabbing incident in 2004, and again for 16 months after aggravated assault on his wife in 2009.
Nykänen met millionaire sausage heiress Mervi Tapola in 1999, and they were married from 2001 to 2003. They were divorced in 2003, and remarried in 2004. This marriage was tempestuous and gave rise to many well-publicised incidents: The first reported assault against Tapola occurred in June 2000, following which a restraining order was imposed upon Nykänen. In 2004, Nykänen was handed a suspended sentence for assaulting Tapola again. Nykänen had already been accused of assaulting Tapola in 2001, but the charges were withdrawn because Tapola exercised her right to remain silent.
In September 2005, while on probation for another assault, Nykänen was re-arrested four days after his release for again abusing his partner. Nykänen was convicted again and imprisoned for four months on 16 March 2006; Soon after that he stabbed a man in a pizza restaurant in Korpilahti. In the summer of 2009 Tapola (then Tapola-Nykänen) petitioned for divorce a 14th time, but cancelled it.
On Christmas Day 2009 Nykänen allegedly injured his wife with a knife and tried to throttle her with a bathrobe belt. He was charged for attempted manslaughter and held in custody by Tampere police, but was released on 28 December after charges were dropped for insufficient evidence. On 24 August 2010 Nykänen was convicted of grievous bodily harm and sentenced to 16 months in jail and ordered to pay 5,000 euros in compensation to his wife for pain and emotional suffering, and 3,000 euros for legal expenses. In August 2010 Tapola made a 15th request for divorce.
On 24 August 2004, Matti Nykänen was arrested on suspicion of attempted manslaughter of a family friend after losing a finger pulling competition in Tottijärvi, Nokia. He was found guilty of aggravated assault and sentenced to a 26-month jail term in October 2004. As it was a first offence, he was released from jail in September 2005.
When Nykänen's ski jumping career was drawing to a close, a group of businessmen proposed to make him a singer. His first album Yllätysten yö was released in 1992 and sold over 25,000 copies. Nykänen became the second Olympic gold medalist after Tapio Rautavaara to be awarded a golden record in Finland. The next album Samurai (1993) was not as successful.
At the end of the 1990s, due to serious financial problems, Nykänen worked as a stripper in a Järvenpää restaurant. The restaurateur was reproached for exploitation of Nykänen.
In 2002 Nykänen made a comeback as a singer and released the single "Ehkä otin, ehkä en". He also gave his name to a cider brand with the same advertisement slogan. In 2006 Nykänen released his third studio album Ehkä otin, ehkä en. Most of his musical career Nykänen has worked with professional musician Jussi Niemi. Nykänen has toured Finland performing 2 to 3 times a week with the Samurai ensemble led by Niemi.
A movie about the life of Matti Nykänen simply called Matti was released in 2006, with Finnish actor Jasper Pääkkönen cast as Nykänen. The movie concentrated on Nykänen's exploits beyond the ski-jumping hills.