"This is the first time that I've ever won this and I'm just losing my mind," Swift said, as she fought back tears.
Taylor Swift Celebrates 20 Million Sales in London
Lambert retained her crown as top female vocalist and her wistful tune "The House That Built Me" was honored for single, song and video of the year at the 46th annual awards ceremony.
The award for single goes to the artist and producer, whereas the trophy for best song is given to the artist and composer.
Lambert, a 27-year-old Texan, went into the ceremony with a leading seven nominations, including two in the video category.
Miranda Lambert: The Billboard Cover Story
The country trio Lady Antebellum won trophies for album and vocal group of the year and Brad Paisley was named top male vocalist for the fifth consecutive year. The award for top new artist went to The Band Perry, a sibling trio from Mississippi.
Kenny Chesney, with five nominations, and Keith Urban, with three, went home empty-handed.
The announcement of winners took second place to a string of performances divided between two hotel venues, the MGM Grand and Mandalay Bay. The winner of the first award was not revealed until almost an hour into the three-hour ceremony.
The show was hosted by Reba McEntire for the 13th year. She was joined by first-timer Blake Shelton, Lambert's fiance.
(Reporting by Dean Goodman in Los Angeles and Tim Pratt in Las Vegas; Editing by Paul Simao and Bill Trott)
COPYRIGHT: (c) Reuters 2011. All rights reserved. Republication or redistribution of Reuters content, including by caching, framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.