Year 1184 (MCLXXXIV) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar.
- May 20 – Diet of Pentecost: Emperor Frederick I (Barbarossa) organises a conference in Mainz. During the diet Frederick negotiates with Henry the Lion about an anti-French alliance with England.
- June 15 – Battle of Fimreite: King Sverre of Norway defeats and kills his rival, Magnus V (Erlingsson) near Fimreite. Sverre takes the throne and becomes sole ruler of Norway (until 1202).
- June – July – Almohad forces reconquer the Alentejo (except for Évora), and besiege Lisbon on land and blockade the port with their navy. A Portuguese soldier manages to swim to the largest ship of the fleet and to sink it. This ship was so tall, it would have allowed the Muslims to easily reach the walls of the city. The next day, the Almohads have to retreat, taking with them a number of civilian captives.
- Siege of Santarém: Almohad forces under Caliph Abu Yaqub Yusuf march towards Badajoz and besiege Santarém, which is defended by King Afonso I (the Conqueror). Upon hearing of Abu Yusuf's attack, Ferdinand II of León marches his army to Santarém to support his father-in-law, Afonso. Abu Yusuf, in an attempt to break the siege, is wounded by a crossbow bolt and dies on July 29.
- October 29 – The 18-year-old Prince Henry, the second son of Frederick I, is engaged to Princess Constance, heiress to the Kingdom of Sicily, at Augsburg in the episcopal palace.
- The city of Abbeville receives its commercial charter by King Philip II (Augustus).
- January 2 – Theodora Komnene, duchess of Austria
- January 13 – Gerard la Pucelle, English bishop (b. 1117)
- February 16 – Richard of Dover, English archbishop
- February 21
- March 27 – George III, king of Georgia (House of Bagrationi)
- March 28 – Eckebert (or Egbert), German Benedictine abbot
- June 15 – Magnus V (Erlingsson), king of Norway (b. 1156)
- July 29 – Abu Yaqub Yusuf, Almohad caliph (emir) (b. 1135)
- September 30 – Arnold of Torroja, Catalan Grand Master
- October 24 – Siegfried, prince-archbishop of Bremen (b. 1132)
- November 15
- November 18 – Josceline de Bohon, English bishop (b. 1111)
- December 17 – Simon de Tosny, Norman-Scottish bishop
- Abu al-Bayan ibn al-Mudawwar, Jewish physician (b. 1101)
- Agnes of Antioch, queen of Hungary (approximate date)
- Aindréas of Caithness, Gaelic-Scottish monk and bishop
- Grimaldo Canella, Italian nobleman (House of Grimaldi)
- Li Tao (or Renfu), Chinese historian and writer (b. 1115)
- Pedro Fernández de Castro, Spanish nobleman (b. 1115)
- Sasaki Hideyoshi, Japanese nobleman and samurai (b. 1112)
- Taira no Atsumori, Japanese warrior and samurai (b. 1169)
- Taira no Koremori, Japanese nobleman (approximate date)
- Taira no Tadanori, Japanese warrior and general (b. 1144)
- William de Vesci, High Sheriff of Northumberland (b. 1125)