Heynen started out his career as a volleyball coach in his hometown club Noliko Maaseik.
In 2005 he became assistant coach and a year later - a head coach.
During his six-year work at the club, his team won four Belgian Championships, five Belgian Cups and four Supercups.
Additionally Heynen was twice named Belgian Coach of the Year in 2009 and 2011.
In 2012 he left his hometown club and joined Turkish club Ziraat Bankası Ankara, which he coached in the season 2012/2013.
In December 2013 he was named a new coach of Transfer Bydgoszcz, PlusLiga.

In February 2012 he became a head coach of Germany national team.

At the World Championship 2014 his team beat France in 3rd place match and won bronze medal.
In 2017 he took over Belgian national team.
On 7 February 2018 Heynen was chosen as the new head coach of Poland men's national volleyball team.
At the World Championship 2018 in Italy, Poland led by Heynen beat Brazil in the final, defended the World Championship 2014 title, and achieved 3rd World Champion title in total.
In 2019 Heynen coached Poland to the European Championship 2019 bronze medal by beating France in 3rd place match and losing only to Slovenia in the semifinal.
At the FIVB World Cup 2019 his team lost only against USA and Brazil and evenutally was placed 2nd in the competition, winning the silver medal.
In November, 2019 he became a head coach of Sir Safety Conad Perugia.
In the season 2019/2020 Sir Safety Conad Perugia coached by Heynen achieved the Italian SuperCup after defeating Modena Volley in the final.
Heynen started out his career as a volleyball coach in his hometown club Noliko Maaseik. In 2005 he became assistant coach and a year later - a head coach. During his six-year work at the club, his team won four Belgian Championships, five Belgian Cups and four Supercups. Additionally Heynen was twice named Belgian Coach of the Year in 2009 and 2011. In 2012 he left his hometown club and joined Turkish club Ziraat Bankası Ankara, which he coached in the season 2012/2013. In December 2013 he was named a new coach of Transfer Bydgoszcz, PlusLiga.
In February 2012 he became a head coach of Germany national team.
At the World Championship 2014 his team beat France in 3rd place match and won bronze medal. In 2017 he took over Belgian national team. On 7 February 2018 Heynen was chosen as the new head coach of Poland men's national volleyball team. At the World Championship 2018 in Italy, Poland led by Heynen beat Brazil in the final, defended the World Championship 2014 title, and achieved 3rd World Champion title in total. In 2019 Heynen coached Poland to the European Championship 2019 bronze medal by beating France in 3rd place match and losing only to Slovenia in the semifinal. At the FIVB World Cup 2019 his team lost only against USA and Brazil and evenutally was placed 2nd in the competition, winning the silver medal. In November, 2019 he became a head coach of Sir Safety Conad Perugia. In the season 2019/2020 Sir Safety Conad Perugia coached by Heynen achieved the Italian SuperCup after defeating Modena Volley in the final.
Vital Heynen