Sam Smith, a 21-year-old singer from London with milk-white skin and a tightly swirled pompadour, has made a name for himself as the soulful guest vocalist for dance music's new wave, including breakout electronic group Disclosure, producer Naughty Boy and disco veteran Nile Rodgers. Now, with a debut solo album and tour on the way, he's attempting to go it alone.

The transition from guest star to solo act can be difficult, but plenty of people are betting on his success. In December, he won the 2014 Brits Critic's Choice Award and earlier this month, he won the BBC's "Sound of 2014" music critics poll, which often predicts commercial success. (Past winners include Adele, 50 Cent and Ellie Goulding.)

He's also demonstrated strong ticket sales. Most of his European tour dates have sold out well in advance. All of his U.S. performances sold out last year—including two nights at the Troubadour in West Hollywood, the first of which sold out in less than 24 hours. He recently announced a 10-city North American tour to promote his forthcoming album, "In the Lonely Hour," due out in the U.S. on June 3. The San Francisco date sold out in a day.

Critics praise the fluid quality of Mr. Smith's voice as well as his emotional lyrics and almost bashful stage presence.

Over the next six months, Capitol Records will shift from coordinating buzzy collaborations to launching Mr. Smith's solo career, culminating in the release of his album. "We've had the big collaborative feature songs, but now we're moving into Sam's own music," said Greg Thompson, executive vice president of Capitol Music Group.

Before the album makes its debut, the label plans to release an EP in February in the U.S., and then have Mr. Smith begin touring while his songs are promoted on college radio. "You need that time to drum up people's appetite," Mr. Thompson said.

The label is counting on concerts to get the word out on Mr. Smith. "Live exposure will be key," Mr. Thompson said.

Growing up in a small town 25 miles north of London, Mr. Smith began training as a jazz singer when he was 8 and had his first manager by age 12. He listened exclusively to female "power singers" until about a year ago, he said, such as Whitney Houston, Chaka Khan and Amy Winehouse, thus the soul and gospel undertones in his music. At 18, he moved to London to tend bar while playing gigs around the city. He met Disclosure in the fall of 2012 through common managers who suggested he sing over the duo's new track "Latch." The song became the first single from Disclosure's debut album "Settle," which received a 2013 Grammy nomination for Best Dance Album.

"I was still working in the bar when the single came out," Mr. Smith said. "It was the strangest feeling. I was behind the bar, glancing around as the song clicked up the charts, having no clue what I was supposed to do."

Soon after Mr. Smith recorded with Disclosure, Nick Raphael, the U.K. president of Capitol Records, asked to visit the artist and offered to sign him within three days. By December, Mr. Smith had quit his bar job and begun preparing a single, "Lay Me Down" and an EP titled "Nirvana." Neither made big waves in the U.K., but "Latch" catapulted Mr. Smith into the global spotlight.

To date, the song's music video has been viewed more than 26 million times on YouTube. After it went viral, Mr. Smith released an acoustic version that features just his vocals and has been viewed more than 1.5 million times. The song reached No. 11 on the U.K. singles chart and led to another collaboration, "Together," that featured Nile Rodgers and Jimmy Napes. In May, his song with Naughty Boy, "La La La," dethroned Daft Punk's megahit "Get Lucky" by capturing the No. 1 spot on Britain's Billboard Chart. It has sold 1.3 million copies in the U.K. and the music video has been viewed more than 224 million times on YouTube.

Mr. Smith completed his album just before the new year and said it is quite different from his club-friendly music. Placing an emphasis on lyrics, it will play like a diary and offer intimate details about his life. The title, "In the Lonely Hour," stems from the larger theme of unrequited love. Mr. Smith has never been in a relationship, he said, and wanted to be a voice for people who "haven't been loved back."

He said it won't sound like a throwback album, despite his recent work with trendy disco-inspired artists.

"People are afraid of being current," he said. "But I don't want my music to sound like it's from the past. I want it to sound like 2014. I'm not embarrassed about that. I love the charts. I live for the charts. I'm going to make a T-shirt that says 'Top 40.'

He pauses. "But everyone would probably think I'm being ironic, wouldn't they?"