| Reign | From November 17, 1592
- until July 24, 1599 in Sweden From August, 1587 - until April 19, 1632 in Poland |
| Coronation | On February 19, 1594 in Sweden.
December 1587 in Poland |
| Royal motto | "Pro jure et populo" ("For justice and people") |
| Consorts | Anna of Austria
Constance of Austria |
| Royal House | Vasa |
| Predecessors | John III in Sweden
Stephen Bathory in Poland |
| Successors | Charles IX in Sweden
Ladislaus IV in Poland |
| Date of Birth | June 20, 1566 |
| Place of Birth | Gripsholm Palace, Sudermannia |
| Date of Death | April 19, 1632 |
| Place of Death | Warsaw, Poland |
| Place of Burial | Cathedral of Krakow |
Sigismund I of Sweden, (June 20, 1566 - April 19, 1632), was the son of John III of Sweden (1537-1592), of the House of Vasa, and his wife Katarina of Poland (1526-1583). He ruled as King Sigismund III of Poland or Zygmunt III of Poland from 1587 to 1632 and as King Sigismund I of Sweden from 1592 until he was deposed in 1599.
His mother was the daughter of Sigismund I the Old and his wife Bona Sforza. The Jogailos royal house of Lithuania had held the crown of Lithuania-Poland Commonwealth since the first ruler Wladislaw Jogaila had received it via his wife Hedwig in 1383. Sigismund was elected king of Lithuania-Poland Commonwealth in 1587.
He married, firstly, on May 31, 1592, Anna of Austria (1573 - 1598), daughter of Archduke Karl II of Austria (1540-1590) and his wife´Maria Anna of Bavaria (1551-1608).
Their children were:
He married, secondly, on December 11, 1605, his first wife's sister, Constance of Austria (1588 - 1631).
Their children were:
| Preceded by: John III | List of Swedish monarchs |
Succeeded by: Charles IX |
| Preceded by: Stephen Bathory | List of Polish rulers | Succeeded by: Ladislaus Vasa |