Lambert called out the actors of the box office hit for "pretending to be singers".
Sharing his thoughts about the movie on Twitter, Lambert criticised the film for its lack of vocal talent and approach in several tweets on Sunday (December 30).
He wrote: "Les Mis: Visually impressive w great Emotional performances. But the score suffered massively with great actors PRETENDING to be singers."
"Hollywoods movie musicals treat the singing as the last priority (sic)."
He continued: "With that cast, they should have studio recorded and sweetened the vocals. I felt like I should ignore the vocals and focus on the emotional subtext - but the singing was so distracting at times it pulled me out.
"The industry will say 'these actors were so brave to attempt singing this score live' but why not cast actors who could actually sound good?"
"Sorry for being so harsh but it's so True!"
The singer did however praise the likes of castmembers Helena Bonham Carter and Sacha Baron Cohen, calling them "great".
Watch the stars of Les Misérables talk to Digital Spy below:
Photo gallery - Les Misérables' world premiere in London: