Oil-rich South Sudan secured independence from its northern neighbour Sudan in 2011 but plunged into civil war two years later after violence erupted between troops loyal to Kiir and his ex-deputy-turned-rival Riek Machar.
In August, Kiir announced the extension of his transitional government's time in office for another two years, meaning elections would be held in December 2024.
On Tuesday, his party, the Sudan People's Liberation Movement (SPLM), endorsed him as its chairman and by extension presidential candidate in the vote.
"The SPLM Political Bureau decided to nominate comrade Salva Kiir Mayardit as ... the Presidential flag bearer in the national elections at the end of the transitional period," Paul Akol Kordit, SPLM's deputy secretary general for political affairs told a party meeting in Juba.
"This is a collective decision of the SPLM Political bureau. That tells you we have no candidate other than our chairman in the political bureau."
A peace agreement signed in September 2018, the latest in a series since the conflict began in late 2013, is largely holding but the transitional government has been slow to unify the various factions of the military into a single unit, write a new constitution and pave the way to elections.
"I accept the nomination ... to become the flag bearer for the SPLM party in the general elections ... and I promise you that never again will this country go back to war," Kiir said, welcoming his nomination.
On Monday, the party also voted to revoke Machar's membership. Machar had previously defected from the main party in 2013, creating his own faction SPLM-IO, and he stated in October that any attempt to sack him was illegal.
(Reporting by Waakhe Simon Wudu; writing by George Obulutsa; Editing by Aurora Ellis)