Henry was due to work as a TV pundit for the tournament but has decided to swap media duties for a return to the Red Devils' dugout.
What’s been said?
News of Henry’s return was confirmed with a brief statement on Twitter, which read: "Unfinished business. We welcome back Thierry Henry in the staff for Euro 2020."
The former France international became Martinez’s second assistant alongside Graeme Jones in August 2016 and helped oversee a successful qualification campaign for the 2018 World Cup.
Belgium went on to reach the semi-finals in Russia, losing to eventual winners France in the last four before beating England in the third/fourth place play-off.
Jones left the coaching staff after the tournament and Henry was promoted to assistant coach. However, his time in that position was short-lived as he left for Monaco in October.
Henry’s spell at Monaco was also brief, lasting just three months before he was sacked in January 2019. He then moved to MLS side Montreal Impact in November 2019 but stepped down in February this year in order to be closer to his family in London.
The bigger picture
Belgium are considered one of the favourites for the tournament thanks to a golden generation of talent that includes the likes of Kevin De Bruyne, Romelu Lukaku and Eden Hazard.
They have been placed in Group B alongside Russia, Finland and Denmark. Their opening match of the tournament is against Russia in Saint Petersburg on June 12.