The 58-year-old acclaimed film and TV director, known for projects like Wild, Big Little Lies and Sharp Objects, died unexpectedly on Sunday at his cabin outside Quebec City, PEOPLE confirmed.
McConaughey and Leto both starred in 2013's Dallas Buyers Club, which Vallée directed. They both won Academy Awards (for Best Actor and Best Supporting Actor, respectively) for the movie, which also starred Jennifer Garner, Steve Zahn and Denis O'Hare.
"With a gentle hand and heart Jean-Marc was a true receiver," wrote McConaughey, 52, on his Instagram Story Monday. "He didn't romanticize life so much as he saw life romantic — from the struggle to the pain to the wink and the whisper, love stories were everywhere in his eye."
Leto, 50, wrote on Instagram about Vallée, "A filmmaking force and a true artist who changed my life with a beautiful movie called Dallas Buyers Club. Much love to everyone who knew him. Life is precious."
Michael Buckner/Getty via Matthew McConaughey/Instagram
Dallas Buyers Club also won an Oscar for Best Makeup and Hairstyling, and was nominated for Best Editing, Best Original Screenplay and Best Picture.
A year later, his 2014 film Wild based on Cheryl Strayed's memoir earned stars Reese Witherspoon and Laura Dern nominations for Best Actress and Best Supporting Actress. They also worked with him on season 1 of HBO's Big Little Lies.
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"My heart is broken. My friend. I love you," Witherspoon, 45, wrote on social media about his death. She added on her Instagram Story, "I will always remember you as the sun goes down. Chasing the fading light. On a mountain in Oregon. On a beach in Monterey. Making sure we all caught a little magic in this lifetime. I love you, Jean-Marc."
Dern, 54, added on Instagram, "Beautiful Jean-Marc Vallee. The world has lost one of our great and purest artists and dreamers. And we lost our beloved friend. Our hearts are broken." In the comment section, author Strayed said, "We share so many beautiful memories."
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Vallée is survived by his sons Alex and Émile, plus siblings Marie-Josée Vallée, Stéphanie Tousignant and Gérald Vallée.
His longtime producing partner Nathan Ross said in a statement to PEOPLE, "Jean-Marc stood for creativity, authenticity and trying things differently. He was a true artist and a generous, loving guy. Everyone who worked with him couldn't help but see the talent and vision he possessed."
"He was a friend, creative partner and an older brother to me," Ross continued. "The maestro will sorely be missed but it comforts knowing his beautiful style and impactful work he shared with the world will live on."