Marc Johnson -- a professional skateboarder -- has died ... according to his longtime colleague.

Skateboarder Louie Barletta confirmed Johnson's passing on Thrasher Magazine's Instagram. Johnson's cause of death is not known at this time.

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Johnson achieved success during the 2000s ... with Thrasher Magazine naming him its Skateboarder of the Year in 2007.

However, Johnson struggled with addiction during his life and was transparent about his recovery from alcoholism.

Barletta says he saw Johnson shortly before his passing ... and he seemed excited about life ... even handing Barletta a list of his hopes and dreams for the future.

Fellow skateboarder, Steve Caballero, added his own tribute ... writing, “Rest in peace Marc, thank you for your commitment and contribution to skateboarding. Wish this could be avoided and we don’t have to read this but know that you are and were loved. Praying for his close friends and family.”

Johnson was 49.

RIP