In 1969, the Padres joined the ranks of Major League Baseball as one of four new expansion teams, along with the Montreal Expos (now the Washington Nationals), the Kansas City Royals, and the Seattle Pilots (now the Milwaukee Brewers). Their original owner was C. Arnholt Smith, a prominent San Diego businessman and former owner of the PCL Padres whose interests included banking, tuna fishing, hotels, real estate and an airline. Despite initial excitement, the guidance of longtime baseball executives, Eddie Leishman and Buzzie Bavasi, as well as a new playing field, the team struggled; the Padres finished in last place in each of its first six seasons in the NL West, losing 100 games or more four times. One of the few bright spots on the team during the early years was first baseman and slugger Nate Colbert, an expansion draftee from the Houston Astros and still the Padres' career leader in home runs.
The team's fortunes gradually improved as they won five National League West titles and reached the World Series twice, in 1984 and in 1998, but lost both times. The Padres' main draw during the 1980s and 1990s was Tony Gwynn, who won eight league batting titles. They moved into their current stadium, Petco Park, in 2004.
On August 20, 2020, the Padres became the first team in MLB history to hit a grand slam in four consecutive games.
Until 2021, the Padres were the last team in MLB that have yet to throw a no-hitter. The record was broken on April 9, 2021, as Joe Musgrove accomplished the feat against the Texas Rangers, finally ending the longest no-hit drought by a team in MLB history. On September 5, 1997, Andy Ashby took a no-hitter into the 9th inning, which was previously the closest that the team had come to achieving this feat.