MORE THAN 5,000 COLD, WET FANS stood in the April mud and rainy darkness at the Beale Street Music Festival, on the banks of the Mississippi River in Memphis, chanting, "We want Jack! We want Jack!" You'd think this would be manna to a folk-rock god, but, sitting on a sofa in a backstage trailer, Jack Johnson had other ideas. "Music is a secondary thing in my life," he told me.

Some may say that huge success accrues only to the single-minded. But as I followed Johnson, 30, on tour from Memphis to New Orleans and beyond, it was clear that putting music second—actually third, behind his family and the ocean—has a lot to do with how a surfer from Oahu's North Shore who claims not to be a "real singer" has, since 2000, produced three platinum albums, selling more than four million CDs in the U.S. alone. His latest album, In Between Dreams, which debuted in March, streaked to number two on the Billboard chart and by June had already topped more than a million copies.

Johnson may be a bona fide star, but he's an unlikely one. He is not disaffected. Nor is he lovelorn, angst-ridden, or tattooed. His wardrobe consists of loose-fitting jeans, T-shirts, flip-flops, and boardshorts. He wears his hair buzzed, as if he can't really be bothered with hair at all. Women think he's hot—"That's a good-lookin' man," a fan said to me as we walked by on a New Orleans street—but Johnson, who's about six feet tall, has no strut or swagger.

Instead of pop culture, he'd rather talk about Kurt Vonnegut or hunting feral pigs in Hawaii (with a knife and a lot of courage). But he and his band, which consists of bassist Merlo Podlewski, 35, drummer Adam Topol, 39, and, on piano and accordion, his old friend Zach Gill, 30, have become headliners at Bonnaroo and other festivals. In addition to his albums, Johnson recently recorded songs for a forthcoming Brian Grazer–Ron Howard feature film of Curious George. In early August he launched a 35-city tour of the U.S. and Canada, drawing mostly sold-out crowds of 10,000 or more. His popularity has made him new friends like Ben Stiller and earned him a couple of houses in prime locations on Oahu's North Shore and near Santa Barbara, California.

By every conventional measure this is a rocket trip to the A-list. But Johnson prefers to call his rise "an amazing chain of events." While he's not exactly wrong, his wild ride has been less a matter of serendipity than proof that the seeds of luck can fall on fertile ground if you follow your destiny and don't lose your soul, something Johnson has done by keeping salt water in his blood and refusing to forget his roots.