Prior to the war, conflict between the Gungans and Naboo was rare, if not nonexistent. It is unknown how the war began, but the then-current dynasty expired at the height of the war (c. 150 BBY), when the last heir was killed in the fighting. Without a ruler, the Naboo elected a Queen to lead them in the war,
In an effort to turn the tide of the war in their favor, a coalition of Naboo noble houses struck a secret deal with an offworld mercenary group, though the war was resolved without the need for external intervention.
At some point between 135 and , some two decades after the war, certain royal houses struck another secret deal with mercenaries to aid them against the Gungans. The Gungans fought back and eventually prevailed, though they lost many lives and some of their swamp cities.
Very little was made public about this conflict in Naboo society, and in the years to come, the reality behind it was unknown except to those with access to a noble family's archives. The mercenary group had been hired by several noble families in an effort to claim plasma sources from the Gungans. The Houses that contributed most to funding the mercenary army were House Tapalo and House Veruna. Disgusted by this, the patriarch of House Palpatine challenged the leader of House Tapalo to a duel of honor at the Palpatines' ancestral home of Convergence. Palpatine died at Tapalo's blade.
The conflict ended in 121 BBY. Upon the queen's death, the Naboo abolished the hereditary monarchy—in the years to come, Naboo monarchs would be elected.
The mercenary conflict remained a controversial point in Naboo politics: in the election of 65 BBY, information was leaked pertaining to the shady role certain royal houses, then opposed to Bon Tapalo and his plans to open Naboo's economy to the greater galaxy, had allegedly played in the first attempt to recruit mercenaries, discrediting their isolationist stance.
There is contradictory information on whether the Gungan–Naboo War ever occurred. One source states that the war occurred between 150 BBY and 121 BBY. The The New Essential Guide to Alien Species states that there was never a war between the Gungans and Naboo, and Queen Amidala says to Boss Nass in Star Wars: Episode I The Phantom Menace that while the Gungans and the Naboo did not always agree, "our two great societies have always lived in peace."
In 2012, the novel Darth Plagueis mentioned the war. Cosinga Palpatine explains to Darth Plagueis, in a scene taking place in 65 BBY, that, "some two decades after our own conflict with them, the Gungans found themselves embroiled in a war for survival with a mercenary army." Since that would place the first conflict at c. and the second at c. 135 BBY, it is possible that "the Gungan–Naboo War" refers to the overall period of hostilities.
- Inside the Worlds of Star Wars: Episode I
- The New Essential Chronology
- The New Essential Guide to Alien Species