The first serious attempt to land an expansion team for the Phoenix area was mounted by Elyse Doherty and Martin Stone, owner of the Phoenix Firebirds, the city's triple-A minor league baseball team and the top affiliate of the San Francisco Giants. In the late 1980s Stone approached St. Louis (football) Cardinals owner Bill Bidwill about sharing a proposed 70,000 seat domed stadium in Phoenix. It was taken for granted that a domed stadium was a must for a major-league team to be a viable venture in the Phoenix area. Phoenix is by far the hottest major city in North America; the average high temperature during baseball's regular season is 99.1 °F (37.3 °C), and game-time temperatures well above 100 °F (38 °C) are very common during the summer.
Bidwill, with plans already in the works to leave St. Louis, opted instead to sign a long-term lease with Arizona State University to use its Sun Devil Stadium as the home of his soon-to-be Arizona-based NFL franchise. Since baseball-only stadiums were not seen as fiscally viable during that era, this effectively ended Stone's bid.
In the fall of 1993, Jerry Colangelo, majority owner of the Phoenix Suns, the area's NBA franchise, announced he was assembling an ownership group, "Arizona Baseball, Inc.", to apply for a Major League Baseball expansion team. This was after a great deal of lobbying by the Maricopa County Sports Authority, a local group formed to preserve Cactus League spring training in Arizona and eventually secure a Major League franchise for the state.
Colangelo's group was so certain that they would be awarded a franchise that they held a name-the-team contest for it; they took out a full-page ad in the sports section of the February 13, 1995 edition of the state's leading newspaper, the Arizona Republic. First prize was a pair of lifetime season tickets awarded to the person who submitted the winning entry. The winning choice was "Diamondbacks", after the Western diamondback, a rattlesnake native to the region known for injecting a large amount of venom when it strikes.
Colangelo's bid received strong support from one of his friends, Chicago White Sox and Chicago Bulls owner Jerry Reinsdorf, and media reports say that then-acting Commissioner of Baseball and Milwaukee Brewers founder Bud Selig was also a strong supporter of Colangelo's bid. Plans were also made for a new retractable-roof ballpark, Bank One Ballpark, nicknamed the BOB, (renamed in 2005 to Chase Field) to be built in an industrial/warehouse district on the southeast edge of downtown Phoenix, one block from the Suns' America West Arena (now Talking Stick Resort Arena).
On March 9, 1995, Colangelo's group was awarded a franchise to begin play for the 1998 season. A $130 million franchise fee was paid to Major League Baseball. The Tampa Bay Area was also granted a franchise, the Devil Rays (to be based in St. Petersburg), at the same time.
Arizona had originally been intended to join Tampa Bay in the American League. However, five American League teams had threatened to block the league assignments because of concerns that they would have additional games out of their time zone, causing early starts that would decrease revenue and TV ratings. Thus, on January 16, 1997, the Diamondbacks were officially voted into the National League while their expansion counterparts in Tampa Bay were voted into the American League. MLB reserved the right to unilaterally move either the Diamondbacks or Devil Rays to another league within the first five years of existence. After the 2001 season, with the possibility of the Twins and Expos being eliminated, it was possible the Diamondbacks would move to the American League. However, MLB's franchise contraction plans never materialized.
According to the original press release from Colangelo's group (which remained posted on the team website during the first few seasons) the chosen team colors were Arizona turquoise, copper, black and purple. "... Turquoise was chosen because the greenish-blue stone is indigenous to Arizona, copper because Arizona is one [of] the nation's top copper-producing states and purple because it has become a favorite color for Arizona sports fans, thanks to the success of the National Basketball Association's Phoenix Suns." The distinctive "A" logo and color scheme was developed by Campbell Fisher Ditko, a Phoenix-based graphic design firm (which also designed the now-iconic "Streaking Sun" logo for the Suns for the 1992 season).
In the earliest days, the Diamondbacks operated as a subsidiary of the Suns; several executives and managers with the Suns and America West Arena were brought over to the Diamondbacks in similar roles. Members of the Suns team, including Kevin Johnson, Danny Ainge (who actually briefly played baseball at the beginning of his career for the Toronto Blue Jays), Danny Manning and coach Paul Westphal, joined Colangelo and modeled the first prototype Diamonbacks uniforms at a publicity event in November 1995.