Social Democratic Party
Japanese political party
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| 2025 | Mizuho Fukushima and Yuko Otsubaki are up for re-election in the House of Councillors for National Proportional Representation (PR) |
| 2024 | Continued to remain in opposition, with minimal electoral representation, led by Mizuho Fukushima. |
| 2022 | In the House of Councillors elections, the party cleared the minimum two percent voter share, maintaining its legal political party status under party president Mizuho Fukushima. |
| 2021 | Mizuho Fukushima leads the party, winning 1 seat in the House of Representatives election. |
| 2021 | The Social Democratic Party lost one of their two seats in the Japanese general election, significantly reducing their parliamentary representation. |
| September 2021 | Mizuho Fukushima remained the party leader, continuing to represent the party's long-standing commitment to anti-nuclear and pacifist policies during the national political discourse. |
| 2020 | The Social Democratic Party continued to maintain its position as a minor left-wing political party in Japan, with declining electoral influence but still representing progressive political ideals. |
| November 14 2020 | The Social Democratic Party voted to agree to a merger arrangement with the Constitutional Democratic Party of Japan, with most party members planning to join the CDP, though party leader Fukushima opposed the merger and remained with the SDP. |
| February 22 2020 | Mizuho Fukushima returns as Chair of the Social Democratic Party, replacing Seiji Mataichi. |
| 2019 | In the Japanese House of Councillors election, the SDP won four representatives: two in the lower house and two in the upper house. |
| February 25 2018 | Seiji Mataichi was elected unopposed as the new party leader and took office. |
| January 2018 | Tadatomo Yoshida declined to run for re-election when his term expired. |
| 2017 | Continued as an opposition party with minimal electoral representation. |
| 2017 | In the Japanese general election, the party managed to maintain its two existing seats. |
| 2016 | Tadatomo Yoshida leads the Social Democratic Party in the House of Councillors election, securing 2.74% of the national vote and 0.51% of the prefectural vote. |
| 2016 | The SDP signed an agreement with the Democratic, Communist, and People's Life parties to jointly field candidates in 32 single-seat districts for the House of Councillors election. |
| 2014 | Remained in opposition under the leadership of Tadatomo Yoshida, with minimal electoral success. |
| 2013 | The party experiences further electoral decline, winning 2.36% of the national vote and 0.51% of the prefectural vote in the House of Councillors election. |
| 2013 | The party's longtime headquarters in Nagatacho, where the predecessor JSP had been located since 1964, were demolished. The party moved to a smaller office in the same area. |
| October 14 2013 | Tadatomo Yoshida takes over leadership of the Social Democratic Party. |
| July 25 2013 | Seiji Mataichi becomes acting party leader after Mizuho Fukushima's term ends. |
| 2012 | Following the Japanese general election, the party retained only six seats in the Diet: two in the House of Representatives and four in the House of Councillors. |
| 2010 | The Social Democratic Party continues to decline in the House of Councillors election, winning 3.84% of the national vote and 1.03% of the prefectural vote. |
| 2010 | The Social Democratic Party returns to opposition status after leaving the DPJ-led coalition. |
| 2010 | The SDP's participation in the Hatoyama Cabinet concluded. |
| 2010 | Returned to opposition status after leaving the DPJ-led coalition government. |
This contents of the box above is based on material from the Wikipedia article Social Democratic Party (Japan), which is released under the Creative Commons Attribution-ShareAlike 4.0 International License.