Mr Machar says some aspects of the deal have not been implemented
The Sudanese pound will replace the dinar that was introduced in 1992.
Correspondents say many southerners regard the dinar as a symbol of "Arabisation" by the former government.
It will be introduced to the south first where five currencies are currently in circulation, the region's vice-president told the BBC.
The currency conversion, that is expected to cost about $150m, was agreed as part of the deal between the government and southern rebels.
The conflict, which was Africa's longest-running civil war pitted the Muslim north against Christians and animists in the south, leaving some 1.5m people dead.
'No account'
South Sudan's Vice-President Riek Machar said the currency would be commonly known in the south as "the Sudani".
"The currency will help us - we will now have an index for our economy; we'll know how our economy is growing," he told the BBC's Network Africa programme.
"This is one advantage. The 2nd advantage is that people will be confident things are moving forward."
Sabir Mohamed al-Hassan, the central bank governor, said the pound would come into circulation on Wednesday and as from 1 July dinars would no longer be accepted.
The pound is expected to equal 100 Sudanese dinars, Associated Press news agency reports.
In his interview, Mr Machar also denied allegations in the press that he was corrupt, saying he led a hand-to-mouth existence.
"Since I have come back from the bush, I have not opened an account," he said.
"My salary is not that big. I have no luxury or enjoyment. Since the agreement was signed I have not travelled abroad. I am inside the country I am more or less like a sitting duck."
Optimistic
Celebrations are being held in Juba, the capital of the south, to mark the signing of the deal with President Omar al-Bashir and Vice-President Salva Kiir addressing a mass rally.
People have high expectations and thought we would have the magical rod of Moses
Riek Machar
Mr Machar said it has not always been easy for the government as it has had to start developing the region from scratch.
"People have high expectations and thought we would have the magical rod of Moses, which don't have. They expected development to pick up fast.
"[But] it took us time to get to grips with the issues and our plans. Now we will be starting this new year with a lot of confidence and a lot of plans that we will implement," he said.
There were also aspects of the peace agreement that were yet to be implemented, he said.
He mentioned that an administration is yet to be set up for the oil-rich region of Abyei, and a border commission is yet to make its report so the south can get is full share of oil revenues.
La banque centrale du Soudan a mis en circulation de la nouvelle livre soudanaise qui remplace l'actuel dinar soudanais. Cette mesure découle directement des accords de paix signés entre le gouvernement soudanais et l'Armée populaire de libération du Soudan qui clôt 20 ans de guerre civile.

Le dinar était perçu dans le sud comme une manifestation de l'arabisation du Soudan par le gouvernement précédent, et n'était donc pas en circulation dans les régions contrôlées par le mouvement rebelle du sud. Plusieurs monnaies alternatives, dont l'ancienne livre soudanaise, étaient utilisées en lieu et place.

D'après Sabir Mohamed Al Hassan, gouverneur de la Banque centrale du Soudan, le dinar restera en circulation aux côtés de la livre, pour un période de transition de six mois avant son retrait total le 1 juillet prochain.

Le taux de conversion fixé par la Banque centrale est d'une livre soudanaise pour 100 dinars soudanais, et d'une piastre pour 1 dinar. Un dollar US s'échange pour environ 200 dinars.

La Banque centrale du Soudan indique que la nouvelle devise reflétera la vision de paix du Soudan, l'unité dans la diversité, la civilisation, les ressources naturelles et le progrès économique. De nombreux thèmes ont été écartés pour le nouvel habillage des billets, incluant les portraits humains, les références aux guerres et conflits, et les symboles religieux et ethniques.

Le coût de ce changement est estimé à 150 millions USD. Hassan a également indiqué que l'assistance internationale espérée pour couvrir ce coût n'était pas parvenue et que les revenus du pétrole soudanais avaient été utilisés à la place, d'après l'agence Reuters.

Des livraisons de la nouvelle devise ont été envoyées dans le sud, où elle sera d'abord introduite.