The former "American Idol" star empathises with the Brit and understands the intense media scrutiny they are under.
"The media loves something that feels new, and 10 years ago - in America anyway - there wasn't a lot of mainstream music people identifying as gay, so it was a novelty, and I feel there might be some parallels there," he tells NME. "On a personal level, I'm really happy for Sam that they've found their truth and they're feeling liberated by it."
Despite the hurdles Smith has had to face, Lambert believes the singer's openness will help others processing their own sexuality.
"At some point, you have to break through the ceiling and discuss trans or non-binary issues and I'm so proud of Sam," Lambert adds. "They're really doing a bold thing."
Smith also addressed those who have been critical of Smith's decision not to be referred to as "he" or "him."
"If you stop for a minute and make it not about you and put yourself in the shoes of the person that's being talked about and try to understand their experience... you'll realise what's being asked is just that you be a decent human being," he says. "People get defensive, saying, 'How dare you ask me to change the way I think!', and just a little empathy would help."