Saitama Seibu Lions

In 1950, the team became a founding member of the Pacific League. It was then owned by Nishi-Nippon Railroad, which was based in Fukuoka. The team finished sixth that year, and at the end of the season was merged with the Nishi-Nippon Pirates to form the Nishitetsu Lions.

The Nishitetsu Lions called Heiwadai Stadium home for their entire existence. They were one of a dominant team in the Pacific League during the 1950s, winning four pennants, including three straight Japan Series against the Yomiuri Giants behind famed manager Osamu Mihara.

The team struggled through the following decade and did not witness much success on the field. In 1969–1970 the team was caught up in the infamous Black Mist game-fixing scandal, which resulted in four Lions pitchers being banned from NPB for life, as well as other players receiving lesser punishments. These losses decimated the team, which finished the 1970 season in last place.

After a third straight last-place finish, in November 1972 the franchise was sold to the Fukuoka Baseball Corporation, also a part of Nishi-Nippon Railroad. Following the sale, the team was renamed the Taiheiyo Club Lions.

Nishi-Nippon Railroad, founded by Nagayoshi Nakamura, owner of Lotte and the Orions, sold the team's sponsorship rights to Taiheiyo Club, a golf course and resort developer. Through the 1970s, the Lions finished no higher than third.

At the end of the 1976 season, the Fukuoka Baseball Corporation announced that the team's new sponsor was Crown Gas Lighter. With this, the team's name for the upcoming season was changed to the Crown Lighter Lions. At the end of the 1978 season, the team was sold to Kokudo Keikaku (later Kokudo), and then merged into Prince Hotels.

Following the sale of the Crown Lighter Lions and their merging into Price Hotels, the team was renamed the Seibu Lions and relocated to a new ballpark in Tokorozawa, Saitama.

The Lions finished in last place following the 1979 season (as of 2019, this is the last time this has happened to them), and finished in fourth place in 1980 and 1981. However, the following seasons would mark the beginning of a period of sustained success for the team under new manager Tatsuro Hirooka and with star players such as Osamu Higashio and Kōichi Tabuchi. Tatsuro Hirooka told the players that meat and other animal foods increase athletes' susceptibility to injury, and decrease their ability to perform. He required all players to take up a strictly vegetarian diet.[2] The club won two-year straight Japan Series in 1982 and 1983, and went the championship again in 1985, but lost to the Hanshin Tigers who won their first Japan Series title in team history.

Following the 1986 season, the club replaced Hirooka with Masaaki Mori, who was able to sustain the team's prolonged success. Mori won eight league championships, between 1986 and 1988 and 1990–1994, and six Japan Series championships in his nine-year managing career, winning the Japan Series in 1986, 1987, 1988, 1990, 1991, and 1992.

The team gained the moniker "Invincible Seibu" during the 1980s and 1990s due to their sustained domination of the league. The Lions had a powerful lineup in this period, loaded with sluggers such as Koji Akiyama, Kazuhiro Kiyohara and Orestes Destrade. Their defense also benefited from the services of skilled players such as Hiromichi Ishige, Romeo Calhoun, Hatsuhiko Tsuji and catcher Tsutomu Ito. Among the pitchers employed by the Lions in this period was "The Oriental Express" Taigen Kaku, Kimiyasu Kudoh, Hisanobu Watanabe, and relievers Yoshitaka Katori and Tetsuya Shiozaki.

In order to reinforce the affiliation between the team and their home region, the Lions added the prefecture name "Saitama" to their team name in 2008. They were Pacific League Champions that year and went on to win the Japan Series. The team logo and uniforms were further modified for the 2009 season, with the team trading in their traditional light-blue colour scheme for a dark blue design similar to that employed during the Nishitetsu Lions era in the 1950s and 1960s.

Team announced Kazuhisa Inao's No.24 was the first retired number of the Lions on May 1, 2012.

Kazuhisa Inao P Retired May 1, 2012

• Yusei Kikuchi (2019-)

Retired From MLB:

• Frank Howard (1974)
• Kazuhisa Ishii (2002–2006)
• Kazuo Matsui (2004–2010)
• Shinji Mori (2006–2007)
• Daisuke Matsuzaka (2007–2014)

• 
  Yusei Kikuchi
• 
  Daisuke Matsuzaka
• 
  Kazuo Matsui
• 
  Hotaka Yamakawa