The US State Department on Friday said Garang had given Secretary of State Colin Powell a fresh undertaking to tie up a deal this year.
"We hope that we will reach a final, just and comprehensive agreement before the end of the year," said Sudan People's Liberation Army (SPLA) chief Garang after Friday's meeting in Washington with Powell.
Powell attended peace talks in Naivasha on 22 October, saying at the time the Khartoum government and opposition were prepared to negotiate an accord by the end of December.
But both the Sudanese government and Garang's SPLA have played down the importance of meeting the target in peace talks which resume in Kenya on 30 November, after a break for the holy month of Ramadan.
Garang said that he and Sudanese Vice President Ali Osman Mohamed Taha would join the talks on or around 5 December.
The negotiators have three main points to settle - the status of three disputed areas and how to share power and wealth.
Sudan's war erupted in 1983 when Garang's SPLA took up arms to end domination of the mainly Christian and animist south by the Muslim north.
The war has left 1.5 million people dead and four million displaced.
Earlier this month, the deputy leader of the rebel movement said in Cairo that the peace talks were very unlikely to reach agreement by the end of the year.