Panic at the Disco, from left Jon Walker, Ryan Ross, Brendon Uri and Spencer Smith.

Atlantic Records / Jennifer Tzar

ALBANY, N.Y. Panic at the Disco bassist Jon Walker checks in from Miami, where he’s just come back from getting sunburned after an afternoon at the beach. Soon, he’ll put on a fancy suit and tie and hit the stage, where he’ll play for hundreds of young, screaming hipsters.

Such is the life of a 22-year-old rock star. A last-minute addition to the Panic at the Disco lineup, Walker became part of an overnight pop sensation that found itself gracing the cover of national rock magazines when its members were barely out of high school.

Vocalist Brendon Urie, guitarist Ryan Ross and drummer Spencer Smith were 17-year-old buddies from Las Vegas when they suddenly had a No. 1 hit on MTV with the video for “I Write Sins Not Tragedies.” They scooped up Walker when they were in Chicago for a tour stop, replacing original bassist Brent Wilson.

Both the single and the album went platinum, the sort of breakout that’s increasingly rare these days.

“I don’t think we ever expected to make a living making music,” said Walker. “But we’re still young and still having fun, so we’re just trying to enjoy it.”

Three years after their debut album, A Fever You Can’t Sweat Out, the band — which recently dropped the exclamation point at the end of “Panic” — is back, their commercial success now matched by critical praise. Their new album Pretty.Odd is a blend of big hooks, steady piano rhythms and soaring vocal harmonies.

By expanding their sound, Panic at the Disco hopes to avoid the sophomore rut that often plagues quick-success bands.

When creating the new album, the band first began writing concept songs.

But after months of struggling, they decided to abandon that idea and set those songs aside, instead opting to go on pure inspiration rather than over-thinking the process.

“We started listening to a lot of different music, and that came out in the songwriting,” said Walker, who name-checked the Zombies, the Beach Boys and Tom Petty. “A lot of older music inspired us. It wasn’t only the quality of the musicianship back then, but people wrote about something that mattered.”

Pretty.Odd was recorded at the Palms Hotel in the band’s hometown, while the strings and mixing were done in the famous Abbey Road studios in London.

Having the benefit of a full orchestra was a change from the recording of their first album, when they had to call their label “Fueled By Ramen,” to approve $300 to hire a trumpet player.

The album has a definite ’60s sound. The opener, “We’re So Starving,” is a short track, acting as sort of a homage to the beginning of the Beatles’ “Sgt. Pepper’s Lonely Hearts Club Band,” with a live-recording texture and the lyrics, “We’re so sorry we’ve been gone/We were busy writing songs for you.”

The effort seems to have paid off: The month-old Pretty.Odd rode as high as No. 2 on the Billboard album chart; it’s at No. 25 this week. (It’s No. 7 on the rock chart.)

A year ago, Walker wasn’t wearing suits to shows. Instead, he was wearing a psychedelic ringmaster outfit, and the band played among a half a dozen circus performers. Walker admits that the theatricality was intended to add to a show that might have been lacking had it all been based on the music alone.

“We were playing some pretty big venues off of only one album,” he said. “We felt the need to put on as big a show as possible.”

Panic at the Disco is headlining the Honda Civic Tour, which also features Motion City Soundtrack, The Hush Sound and Phantom Planet.

“We thought (teaming with Honda) was a good idea. They were able to help us put on a tour, and kids don’t have to pay a bunch of money,” said Walker.

The tour is a promotional tool for Honda’s hybrid vehicle; the band customized and signed one of the cars, which will be won by a fan. While the tour itself isn’t billed as eco-friendly, Walker said he hopes the show will raise awareness of environmental issues.

“We would definitely like to do our part,” he said. “We hope this helps in its own way.”

Despite the sudden rush of fame, the band’s members have remained essentially the same.

“Fame isn’t really like anything,” said Walker. “We just try to stay normal people. There’s a lot of stuff out there that can make you not normal, but we try to stay away from that and just play music.”

Panic at the Disco and the Honda Civic Tour are at the Bank of America Pavilion, 290 Northern Ave., Boston, Sunday at 7 p.m. Tickets are $32.50 and available through the box office at (617) 728-1600; Ticketmaster at (401) 331-2211 or www.ticketmaster.com