On March 30, 1994, county executive Gary Locke appointed a task force to assess the need for a new baseball stadium to replace the rapidly deteriorating Kingdome.
Many feared that the Mariners would leave Seattle if a new stadium was not built.
In January 1995, the 28-member task force recommended to the King County Council that the public should be involved in the financing of the stadium.
The task force concluded that a sales tax increase of 0.1% (to 8.3%) would be sufficient to fund the stadium.
King County held a special election on September 19, asking the public for this sales tax increase; the measure led early, but was narrowly defeated by one-fifth of one percent.

On October 14, a special session of the state legislature authorized a different funding package for a new stadium that included a food and beverage tax in King County restaurants and bars, car rental surcharge in King County, a ballpark admissions tax, a credit against the state sales tax, and sale of a special stadium license plate.
Nine days later, the King County Council approved the funding package, and established the Washington State Major League Baseball Stadium Public Facilities District to own the ballpark and oversee design and construction.
Taxpayer suits opposing the legislative actions and the taxes failed in the courts.

On September 9, 1996, the site was selected for the new stadium, just south of the Kingdome.
In late fall, several members of the King County Council wrote a letter to the Seattle Mariners, requesting a postponement of the projected $384.5-million stadium project.
In response, Mariners ownership held a news conference stating that they would either sell the team or move it from Seattle.
After a public outcry, the King County Council voted to reaffirm their cooperation with the Mariners in building a new stadium.
Team ownership contributed $145 million to cover cost overruns.

Construction officially began in 1997, with a groundbreaking ceremony on March 8 featuring Mariners star Ken Griffey, Jr. The construction, overseen by Chief Financial Officer (and current team President and minority owner) Kevin Mather, continued through the beginning of the 1999 season.
Its first game was on Thursday, July 15, immediately after the All-Star break; the Mariners lost 3–2 to the San Diego Padres with 44,607 in attendance.

The naming rights were sold to Seattle-based Safeco Insurance in June 1998, who paid $40 million for a 20-year deal.
The 2018 season was the last played under this name, and the Safeco signage was removed from the ballpark beginning that November.
The naming rights were awarded to T-Mobile on December 19, an agreement that will last 25 years, and the name change officially took effect on January 1, 2019.

Ken Griffey, Jr. returned to Safeco Field in 2007 with the Cincinnati Reds (where he had been traded to after the 1999 season) to a hero's welcome.
In commemoration of Griffey's achievements with the team, the Mariners unveiled a new poster that declared Safeco Field "The House That Griffey Built."

The Mariners moved the fences at Safeco Field closer to home plate prior to the 2013 season "to create an environment that is fair for both hitters and pitchers," according to General Manager Jack Zduriencik.
Safeco Field had been considered one of the most pitcher-friendly ballparks in the majors since it had opened.
The center field scoreboard and ad panels were replaced with an 11,435 square foot (1,062.3 m²) board during renovations, becoming the largest among all stadium scoreboards in the major leagues at the time.

After the 2017 season, the field surface, in place since the stadium opened in 1999, underwent its first full replacement.
The infield and foul territory were redone in 2012, but the outfield had never been replaced before the resodding.
On March 30, 1994, county executive Gary Locke appointed a task force to assess the need for a new baseball stadium to replace the rapidly deteriorating Kingdome. Many feared that the Mariners would leave Seattle if a new stadium was not built. In January 1995, the 28-member task force recommended to the King County Council that the public should be involved in the financing of the stadium. The task force concluded that a sales tax increase of 0.1% (to 8.3%) would be sufficient to fund the stadium. King County held a special election on September 19, asking the public for this sales tax increase; the measure led early, but was narrowly defeated by one-fifth of one percent.
On October 14, a special session of the state legislature authorized a different funding package for a new stadium that included a food and beverage tax in King County restaurants and bars, car rental surcharge in King County, a ballpark admissions tax, a credit against the state sales tax, and sale of a special stadium license plate. Nine days later, the King County Council approved the funding package, and established the Washington State Major League Baseball Stadium Public Facilities District to own the ballpark and oversee design and construction. Taxpayer suits opposing the legislative actions and the taxes failed in the courts.
On September 9, 1996, the site was selected for the new stadium, just south of the Kingdome. In late fall, several members of the King County Council wrote a letter to the Seattle Mariners, requesting a postponement of the projected $384.5-million stadium project. In response, Mariners ownership held a news conference stating that they would either sell the team or move it from Seattle. After a public outcry, the King County Council voted to reaffirm their cooperation with the Mariners in building a new stadium. Team ownership contributed $145 million to cover cost overruns.
Construction officially began in 1997, with a groundbreaking ceremony on March 8 featuring Mariners star Ken Griffey, Jr. The construction, overseen by Chief Financial Officer (and current team President and minority owner) Kevin Mather, continued through the beginning of the 1999 season. Its first game was on Thursday, July 15, immediately after the All-Star break; the Mariners lost 3–2 to the San Diego Padres with 44,607 in attendance.
The naming rights were sold to Seattle-based Safeco Insurance in June 1998, who paid $40 million for a 20-year deal. The 2018 season was the last played under this name, and the Safeco signage was removed from the ballpark beginning that November. The naming rights were awarded to T-Mobile on December 19, an agreement that will last 25 years, and the name change officially took effect on January 1, 2019.
Ken Griffey, Jr. returned to Safeco Field in 2007 with the Cincinnati Reds (where he had been traded to after the 1999 season) to a hero's welcome. In commemoration of Griffey's achievements with the team, the Mariners unveiled a new poster that declared Safeco Field "The House That Griffey Built."
The Mariners moved the fences at Safeco Field closer to home plate prior to the 2013 season "to create an environment that is fair for both hitters and pitchers," according to General Manager Jack Zduriencik. Safeco Field had been considered one of the most pitcher-friendly ballparks in the majors since it had opened. The center field scoreboard and ad panels were replaced with an 11,435 square foot (1,062.3 m²) board during renovations, becoming the largest among all stadium scoreboards in the major leagues at the time.
After the 2017 season, the field surface, in place since the stadium opened in 1999, underwent its first full replacement. The infield and foul territory were redone in 2012, but the outfield had never been replaced before the resodding.
T-Mobile Park