A human-rights group said on Tuesday that Muktiram Dahal, 76, had no contact with his son, whose real name is Pushpa Dahal, since he took up arms in 1996 to topple the monarchy and install a communist republic.
"Muktiram Dahal has expressed his willingness to lead the peace march," in April, Human Rights Organisation of Nepal president, Sudeep Pathak, said.
The increasingly deadly conflict between the rebels and security forces has claimed more than 11,000 lives.
Pathak said he met Prachanda's father at his residence in Bharatpur, 190km south of Kathmandu, on Sunday.
"When I asked him to lead a peace march ... to mark international Human Rights Day, Muktiram was very willing to accept," Pathak said.
Killings must stop
Pathak quoted Prachanda's father as saying: "The killings should stop. I am for peace, so I will certainly participate in the peace programme."
"Muktiram also said Prachanda had not met any family member since 1995," Pathak added.
Father of two sons and six daughters, Muktiram lives in his ancestral home in Bharatpur.
The peace rally is expected to take place in eastern Nepal. Organisers said they did not know yet how many days it would take.
The group expects thousands of people to participate in the 1400km east-west march through Nepal.
Late last month, tens of thousands of peace demonstrators rallied in the capital, Kathmandu, calling for an end to the bloodshed.