"No one should stay at home, no one should stay in their offices, because we are all going to march with a single purpose, a purpose that unites us all: to say 'yes' to liberty and 'no' to kidnapping," he said at an event late Monday, according to a presidential statement.
The nationwide demonstration was set to begin at 10:00 am (1500 GMT).
The march was initially called for by ordinary citizens via social networks following the killing of four hostages by the Revolutionary Armed Forces of Colombia (FARC), which had held the men for more than 12 years.
The four were shot during a firefight on November 26 between rebels and security forces in the remote Solano region of southern Colombia. A fifth hostage managed to escape the melee.
The bodies of three of the dead hostages, all of whom were members of the security forces, were each found with a gun shot to the back of the head. The fourth had been shot in the back.
The FARC, believed to have 8,000 members, has been at war with the government since 1964. It began a campaign of kidnappings in the mid-1980s, seizing army hostages to serve as bargaining chips for FARC prisoners.