The 44-year-old Colombian has been called up to drive the #21 DragonSpeed Oreca 07 alongside Memo Rojas and Timothe Buret for what will be his second Le Mans start.
Montoya, who won last year's IMSA WeatherTech SportsCar Championship driving for Acura Team Penske together with Dane Cameron, takes the place of three-time Sebring 12 Hours winner Pipo Derani in the line-up aboard DragonSpeed's lead entry.
Team sources have confirmed that Montoya will drive the car in the double-points FIA World Endurance Championship event on September 19/20.
An official announcement is expected after the team has gone through the official procedures required to change a driver by race organiser the Automobile Club de l'Ouest.
It is understood that Montoya was approached by DragonSpeed boss Elton Julian, whose team also races in the IndyCar Series, after a breakdown in its relationship with Derani.
Montoya's first Le Mans start came with the United Autosports LMP2 squad co-owned by McLaren Racing boss Zak Brown in 2018. He shared a Ligier JS P217 with American Will Owen and Swiss Hugo de Sadeleer (pictured below).
#32 United Autosports Ligier JSP217 Gibson: Huge de Sadeleer, Will Owen, Juan Pablo Montoya
Ashleigh Hartwell / Motorsport Images
They finished fifth in LMP2 on the road, but moved up to third in LMP2 and seventh overall on the disqualification of the G-Drive Racing and TDS Orecas for refuelling system irregularities.
Montoya has focussed on sportscar racing with Penske since the beginning of the Acura programme in 2018 and currently lies seventh in this year's IMSA DPi standings.
He has also won the Rolex 24 at Daytona on three occasions with Chip Ganassi Racing, with which he was racing in the NASCAR Cup.
Montoya has outlined a desire to try to claim the unofficial triple crown of motor racing by adding a Le Mans victory to his 2000 and 2015 Indy triumphs and his 2003 Monaco Grand Prix victory with Williams.
He tested a Porsche 919 Hybrid LMP1 car in Bahrain in November 2015, setting fastest time of the day in the official WEC rookie test.