The 18-year old beat the likes of Katy Perry, Drake, Rihanna and Maroon 5 to the coveted Artist of the Year Award - lifting his mum Pattie Mallette up the air after his name was read out, as he invited her to join him on stage.
JB was clearly taken back by his win, struggling to get his words out during his acceptance speech.
He said: "This is my mum, this is my mum. She's little, but she's beautiful. And thank you so much. First of all, I wanna say... they told me to... I can't even think, I mean, I'm so blown away right now."
Bieber then turned to Mallette and said: "I want to thank you for just believing in me. I want to thank everyone, just everyone. I'm at a loss for words.
"I just want to say... it's hard growing up with everything going on, with everyone watching me. I just wanted to say that as long as you guys keep believing in me, you know, I will never... I will always make you proud.... So thank you so much. I love you."
The Boyfriend singer also took home trophies for Favourite Male Artist - Pop/Rock and Favourite Album - Pop/Rock for Believe.
His Beauty And A Beat collaborator Nicki Minaj also won two awards for Favourite Album - Rap/Hip-Hop for Pink Friday: Roman Reloaded and Favourite Artist - Rap/Hip-Hop.
In her speech for the latter prize, Minaj stated: "Barbz, I know you're somewhere out there watching this on TV. I love you so much, you are so passionate and inspiring.
"Thank you so much for voting your little fingers off... I've got to thank anyone who had anything to do with my career ever."
Nicki then thanked her continued her best friend Taeisha, her hairdresser Terence, "who I never thank", Lil Wayne and her label Young Money Entertainment, before adding: "Thank you to the AMAs, you guys always have the best shows."
However, it was PSY who stole the show yet again, this time, teaming up with MC Hammer for a rendition of his smash hit single Gangnam Style mashed with the rapper's tune 2 Legit 2 Quit to close the bash - with the pair both wearing 'Hammer pants.'
Full list of 2012 AMA winners:
Artist of the Year
Justin Bieber - WINNER
New Artist of the Year
Carly Rae Jepsen - WINNER
Favourite Male Artist - Pop/Rock
Justin Bieber - WINNER
Favourite Female Artist - Pop/Rock
Katy Perry - WINNER
Favourite Band, Duo or Group - Pop/Rock
Maroon 5 - WINNER
Favourite Album - Pop/Rock
Justin Bieber - Believe - WINNER
Maroon 5 - Overexposed
Nicki Minaj - Pink Friday: Roman Reloaded
One Direction - Up All Night
Favourite Male Artist - Country
Luke Bryan - WINNER
Favourite Female Artist - Country
Taylor Swift - WINNER
Favourite Band, Duo or Group - Country
Zac Brown Band
Lady Antebellum - WINNER
Favourite Album - Country
Luke Bryan - Tailgates & Tanlines
Lionel Richie - Tuskegee
Carrie Underwood - Blown Away - WINNER
Favourite Artist - Rap/Hip-Hop
Nicki Minaj - WINNER
Favourite Album - Rap/Hip-Hop
J Cole - Cole World: The Sideline Story
Drake - Take Care
Nicki Minaj - Pink Friday: Roman Reloaded - WINNER
Favourite Male Artist - Soul/R&B
Usher - WINNER
Favourite Female Artist - Soul/R&B
Beyoncé - WINNER
Mary J Blige
Favourite Album - Soul/R&B
Chris Brown - Fortune
Rihanna - Talk That Talk - WINNER
Usher - Looking 4 Myself
Favourite Artist - Alternative Rock
The Black Keys
Linkin Park - WINNER
Favourite Artist - Adult Contemporary
Adele - WINNER
Favourite Artist - Latin
Shakira - WINNER
Favourite Artist - Contemporary Inspirational
tobyMac - WINNER
Favourite Artist - Electronic Dance Music (EDM)
David Guetta - WINNER
Watch MTV News on the hour every hour on MTV - Sky Channel 126 and Virgin Channel 134