His star, near the renowned Stella Adler Academy of Acting, where Ruffalo studied, was unveiled on Thursday.
"I came here at 18, and I believed in myself ... in a way that only an 18-year-old can, totally oblivious to the fact of how freaking hard it was going to be," Ruffalo said.
The 56-year-old has received four Oscar nominations, the latest in January for his performance as a debauched lawyer in the 2023 comedy-drama Poor Things.
He had an emotional reunion with his former cast mate Jennifer Garner at the ceremony.
Garner said to work with Ruffalo "is to love you".
"I don't care what anyone says. You allow yourself to be fully known by your colleagues, by the audience, by the world," Garner said.
"Your work on Poor Things deserves all of the awards, all of them, but the real success is in how thrilled and delighted your colleagues are to have the opportunity to lift you up and celebrate you."
To all young actors who "come to Los Angeles with a dream," Ruffalo said, Â "there's nothing difficult in life that isn't in some way worth it".
He dedicated the star to his audience, fans, artist colleagues and friends.
"A career as an actor is never done alone. It takes so many people to do it," he said.
"I want to say the star, it's not just mine, it's yours, it's you folks out there."
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