Salva Kiir Mayardit has been chosen as successor to Sudan's former rebel leader John Garang, following his death in a helicopter crash.
As deputy leader of the Sudan People's Liberation Movement (SPLM), Mr Kiir had recently been sworn in as vice-president of southern Sudan.
He will now replace Mr Garang as the vice-president of Sudan and president of the south.
Analysts say his nomination by the SPLM signals a clear desire for continuity in the implementation of the peace agreement signed by Mr Garang in January, reports BBC.
The speed with which the SPLM named Salva Kiir as Garang's successor confirms his status as a unifying figure in a group composed of tribes prone to commercial rivalries and harassed by pro-Khartoum militias.
"He's a pragmatic military man, a commander on the ground, who has the personality to bring people together," said Kenyan diplomat Bethuel Kiplagat.
"He's a stabilising influence," said veteran Sudan watcher and aid worker Dan Eiffe. "It's going to be a different style of leadership. It will be more of a group."
Kiir, a military man in his 50s, was appointed on Monday after former rebel leader Garang died when a Ugandan helicopter he was travelling in went down in bad weather.
Analysts say Kiir may bring a more collegial style to the SPLM leadership which Garang had long dominated with a widely-resented, centralised style of decision-making much in evidence during his negotiation of a January peace accord.
"The SPLM is likely to be more unified under Salva and the speed with which he was appointed reflects that," said Horn of Africa expert Alex de Waal.
"Garang was a controversial and not particularly liked figure. Salva is a much more unifying figure."
The SPLM fought a civil war for more autonomy for the largely animist and Christian south for 21 years. Two million people were killed and four million uprooted in the conflict, informs Reuters.