Former France and Arsenal star Henry was suspended and later axed by Monaco after just two wins in the league since his arrival in October.
Jardim, who led Monaco to the French title in 2017, is returning to the club only three months after he was dismissed following a dreadful start to the season.
His first game back in charge will be Tuesday's League Cup semi-final against Guingamp, as Henry's former assistant Franck Passi oversaw the trip to fellow strugglers Dijon.
The abject nature of this latest defeat further emphasised Monaco's perilous position in the table where they remain second from bottom, a point above last-placed Guingamp.
"We're giving everything but it's not enough," said Monaco captain Radamel Falcao. "Each player has to continue to give more, all of us together. We're all in the same boat.
"We didn't manage to change things with Thierry Henry and now we must carry on with a better spirit and all fight together."
Dijon's Kwon Chang-hoon notched his first league goal since May, having recently returned from an Achilles injury, with a calm finish on 24 minutes after a static Naldo played the South Korean onside.
Monaco were reduced to 10 men on the hour when Brazilian Naldo saw red for a clumsy challenge on Julio Tavares, and another defensive lapse allowed Naim Sliti to wrap up what was just Dijon's second league win since August.
It was Naldo's second red card in a week after he was also dismissed in the 5-1 loss to Strasbourg last Saturday.
"We had chances just like in the past four of five matches but we always make a mistake that kills us," said Passi, who refused to be drawn on his own future.
"We let the other team go ahead and we're chasing after the result and that obviously makes it harder," he added.
"These players have the quality. They have what it takes to stay up but they just need for things to click and for it to happen quickly."
Youcef Atal and Allan Saint-Maximin scored for Patrick Vieira's Nice in a 2-0 home win over Nimes, while Kenny Lala fired home a sweet half-volley with practically the final kick to give Strasbourg a 1-0 victory over Bordeaux.
Reims climbed into the top half as a 1-0 win at Guingamp stretched their unbeaten run to six matches.
On Sunday, leaders Paris Saint-Germain will host Rennes without the injured Neymar.
The world's most expensive player limped out of Wednesday's French Cup win over Strasbourg after hurting his foot, an injury similar to the one that ruled him out for more than two months last season.
PSG coach Thomas Tuchel has said it is "still too early" to assess the seriousness of Neymar's injury, leaving the French giants sweating over his fitness ahead of their Champions League clash with Manchester United next month.
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