Saitama Seibu Lions

In 1950, the team became a founding member of the Pacific League. It was then owned by a private railroad company Nishi-Nippon Railroad, well known as "Nishitetsu", which was based in Fukuoka in Kyushu Island, the western erea of Japan (Nishi-Nippon). The Clippers name was chosen as Nishitetsu was in charge of Pan American Airlines' Japanese operations (back then, Pan Am's jets were known as "Clippers" due to them being aeronautical Boeing 314 Clipper).[2] The team finished sixth that year, and at the end of the season, Nishitetsu was merged with another professional baseball club in Fukuoka, the Nishi-Nippon Pirates, which belonged to the Central League and managed by a local newspaper company the Nishinippon Shimbun. The new club was to form the Nishitetsu Lions. Thus the Lions name was adopted and has been retained up to today as the name of the franchise.

The Nishitetsu Lions called Heiwadai Stadium home for their entire existence. They were one of the most dominant teams in the Pacific League during the 1950s, winning four pennants, including three straight Japan Series against the Yomiuri Giants behind famed manager Osamu Mihara; their last championship in Fukuoka came in 1958; after which Mihara left for the Taiyo Whales and led them to a Japan Series championship over the Daimai Orions in 1960.

The team struggled through the following decade and did not witness much success on the field. In 1969 and 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 the team would not recover from for the rest of their time in Fukuoka, which finished the 1970 season in last place.

After a third straight last-place finish, and with Nishi-Nippon not wanting to do with anything to the team due to the Black Mist Scandal, in November 1972, the franchise was sold to the Fukuoka Baseball Corporation, a shell company within Nishi-Nippon Railroad. Following the sale, the team was renamed the Taiheiyo Club Lions.

Nishi-Nippon Railroad, founded by Nagayoshi Nakamura, then owner of Lotte Corporation and the Orions, sold the team's sponsorship rights to Taiheiyo Club, a golf course and resort developer in 1973. The Lions, still smarting from the after-effects of the Black Mist Scandal, finished no higher than third throughout the 1970s.

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. On October 25, 1978, 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 Prince Hotels, the team was renamed the Seibu Lions and relocated to a new ballpark northward in Tokorozawa, Saitama, west of the Tokyo area. Fukuoka would be left without an NPB team until 1989, when the erstwhile Nankai Hawks were bought by Daiei (they are now owned by the SoftBank Group) and moved to the Lions' former stadium, Heiwadai Stadium.

The Lions finished in last place in 1979 (something the team would not do again until 2021), 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.[3] The club won consecutive Japan Series in 1982 and 1983, and went to the Japan Series again in 1985, but lost to the Hanshin Tigers, who won their first and so far only Japan Series title in team history. That Japan Series was also notable for the Tigers also breaking tradition by becoming the first Central League club to use the designated hitter during the Japan Series, prior to the NPB requiring its use during the Japan Series in Pacific League stadiums in 1990 (with it eventually being also used in interleague play when it was introduced in 2005).

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. Between 2010 and 2019, the Lions made the Pacific League Climax Series 1st stage 5 times, (2010, 2011, 2012, 2013, 2017) but lost to the Chiba Lotte Marines in 2010 and 2013, the Tohoku Rakuten Golden Eagles in 2017, and to the Fukuoka SoftBank Hawks in 2011 and 2012. They made the Final Stage twice in back to back years in 2018 and 2019, but lost to the Hawks on both occasions. In 2020, the team finished in 3rd place, but was unable to make the playoffs. Due to the COVID-19 pandemic, the Pacific League removed the First Stage of the playoffs; only the top 2 teams in Pacific League made the playoffs, while Central League removed it entirely, instead opting to send the regular season champion (Yomiuri Giants) straight to the Japan Series. In 2021, the Lions finished in 6th and last place for the first time since 1979 with a 55–70–18 record.

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