Swift leaped from her seat with her arms in the air and jumped up and down before hugging her mother and good friend Tim McGraw.
Swift won the award for the second time. The international crossover sensation who has sold more than 20 million albums by the age of 21 also won the CMA's top honor in 2009.
Swift becomes the second woman to win entertainer of the year twice at the CMAs, joining Barbara Mandrell.
Blake Shelton and Kenny Loggins opened an eclectic Country Music Association Awards with a high-energy version of Loggins' hit "Footloose," but Hank Williams Jr. stole the show.
Williams appeared during the opening skit Wednesday night with hosts Brad Paisley and Carrie Underwood, who lampooned his recent troubles with ESPN and his "Monday Night Football" theme song. Paisley brought out an acoustic guitar and began his own version of "All My Rowdy Friends Are Coming Over Tonight."
"Are you ready for an awards show ... This is rockin' Bradcephus," Paisley sang before Underwood warned him he might draw Williams' ire.
As they spoke, Williams quietly walked up behind the hosts to the roar from the crowd. Asked if he wanted to say something, Williams said, "No," to the delight of the crowd.
The theme of the night quickly became country crossovers with Jason Aldean and Kelly Clarkson teaming to win musical event of the year on "Don't You Want to Stay" and Kenny Chesney and Grace Potter winning video of the year for their steamy "You and Tequila."
The Band Perry won single of the year for their surprise breakthrough "If I Die Young."
On the red carpet, the genre-mixing was in high gear. Lionel Richie was the star of the night, receiving excited hugs and informal tributes from stars like Lady Antebellum, Darius Rucker and Lambert, who posed for a picture with Richie. Kenny Chesney said he once gave a girl a mixtape of Richie's songs in high school.
The focus of the night is the entertainer of the year where most of country's biggest stars are featured.
Jason Aldean and Shelton are new additions to the category.
"Every few years you kind of start to see a changeover of everything," Aldean said. "You start to see different people getting into categories they weren't before. It's like the changing of the guard a little bit."
The two rising stars got to the ballot by taking very different paths, but they've both created a buzz around these awards and in the industry.
Aldean built his audience on the road, while Shelton capitalized on several high-profile events, including his role as a coach on "The Voice," to raise his profile beyond the traditional country music audience.
Both have had a string of hits, but with markedly different sounds. Shelton, the reigning CMA male vocalist of the year, is a mellow baritone with something of a traditionalist approach spiked by humor. Aldean cranks up the guitars and mines a newer sound.
They face Taylor Swift, Paisley and Keith Urban - all previous winners.
It's often de rigueur to feign indifference at award shows, but in this case both are openly appreciative of what even a nomination in the category means.
"I still think it's early," Shelton said. "I think the exposure I've had on `The Voice' and hopefully the exposure I'm giving Nashville and country music in general is probably the reason why people in the industry said, `Hey, you know what? Throw that guy in there.' I'm honored by that."
Defending entertainer Paisley, who co-hosts the awards with Carrie Underwood live at 8 p.m. EST on ABC, says winning the award is just as cool as he imagined it would be as he patiently waited his turn.
"I really feel like there's only been 44 of those handed out, and to someone who really tries to entertain the people that spend the money on the tickets to a concert, it just felt like the award to win," Paisley said. "For so many years I wondered if I would get that. And, you know, in that sense it's one of the proudest things I've ever accomplished, being one of the names written on one of those plaques."
Swift, Aldean, Paisley and Shelton are the top nominees with five apiece.
Most of country's top stars were making appearances on the red carpet Wednesday evening before the show.
Shelton arrived with his wife and fellow nominee Lambert, who showed up in a stunning strapless silver-sequined dress, before slipping away to prepare to open the show alongside Loggins.
All five entertainer nominees were scheduled to perform on a show that promises to the showc. Richie will make his first appearance at the awards since 1986, singing selections from his new country duets album with Rascal Flatts, Darius Rucker and Little Big Town.
Faith Hill will debut a new single, "American Idol" winner Scotty McCreery will take to the stage in front of millions of viewers again and Potter will join Chesney on "You and Tequila."