Sudan's official news agency SUNA said Bashir signed on Sunday an order to extend the ceasefire until October 31.
The decision to extend the ceasefire from July 2 to October 31 comes days before the United States is expected to announce if it will permanently lift a 20-year trade embargo on Khartoum.
Sudan's official news agency SUNA said Bashir signed on Sunday an order to extend the ceasefire until October 31, describing it as "part of the government's initiative to bring peace to Sudan".
In June 2016, Bashir declared a unilateral four-month truce in the three regions, where fighting between government forces and rebels has killed tens of thousands of people.
He extended it in October 2016 to the end of the year and again for a month on December 31. On January 15 he further extended it by six months.
The administration of US President Donald Trump is due to decide on July 12 whether to permanently lift the sanctions imposed on Khartoum in 1997 for its alleged support for Islamist militant groups.
Now slain Al-Qaeda leader Osama bin Laden was based in the Sudanese capital from 1992 to 1996.
Former US president Barack Obama eased the sanctions in January, but made their permanent lifting dependent on Khartoum making progress in five areas during a six-month review period that ends next week.
These conditions include improved access for aid groups, halting support for rebels in neighbouring South Sudan, an end to hostilities in Darfur, Blue Nile and South Kordofan, and counterterrorism cooperation with US intelligence agencies.
The top US envoy to Sudan, charge d'affaires Steven Koutsis, told AFP last month that Khartoum has made "positive" steps towards meeting these five conditions and shown "extreme restraint" in responding to rebel attacks over the past year.
"We have seen that the government has shown extreme restraint even in circumstances where they could have responded under the genus of self-defence," he said in an interview.
Koutsis also said he was hoping that ahead of July 12, Khartoum would extend its unilateral ceasefire "for a minimum six more months".
The conflict in Darfur -- a region of the size of France -- erupted in 2003 when ethnic minority rebels took up arms against Bashir's Arab-dominated government, accusing it of marginalising the region.
Similar conflicts also erupted in Blue Nile and South Kordofan states after neighbouring South Sudan broke away in 2011.
At least 300,000 people have been killed and 2.5 million displaced in Darfur since the conflict began, the UN says.
Thousands more have been killed in Blue Nile and South Kordofan.
Washington has kept the sanctions in place largely in response to the scorched-earth tactics that Bashir's regime has used against the rebels in Darfur.