"He has made tireless work to democratise the country and achieve a transition from totalitarian regime to democratic system of government in our country."
Arman will be challenging Omar Hassan Ahmed al-Bashir, the leader of the ruling National Congress Party and the sitting president since 1993.
If all goes to plan, it will be the country's first full, multiparty poll in 24 years. There was an effectively single-party ballot in 1996 and most opposition parties boycotted elections in 2000.
Arman told the AFP news agency that he was confident he would defeat al-Bashir.
"I was deeply touched by this nomination, and I know it is a serious job and work, and it is part of the struggle that we have been doing for the last 27 years, and I will continue with the same spirit of the SPLM," he said in the southern capital, Juba.
"I am confident that the SPLM can win in the south and at the national level."
The elections were approved as part of the Comprehensive Peace Agreement (CPA) signed in 2005 to end a 22-year civil war.
Two million people were killed and four million fled their homes between 1983 and 2005 as the north and south battled over differences of ideology, ethnicity and religion.
North Sudan is mostly Muslim while southerners are largely Christian and followers of traditional beliefs.
South Sudan election
The SPLM also chose their candidate for the presidency of semi-autonomous South Sudan on Friday.
"We have for the presidency of the government of Southern Sudan a sole candidate - comrade Salva Kiir Mayardit, the chairman of the SPLM," Amum said.
Kiir is already Sudan's vice-president.
The elections for the president of Sudan and the president of South Sudan will be decided by absolute majority. If no gets more than 50 per cent there will be a second round of voting between the top two candidates.
If a northerner becomes Sudan's president, he has to nominate the south's president as his first vice-president, according to the interim constitution. If a southerner wins, he has to appoint a northern vice-president.
Voting is due to take place over three days from April 11, 2010, with the results out by April 18. But the poll has already been delayed several times.
Furthermore, the south of the country is due to hold a referendum on independence from the north in 2011.