The law announced yesterday will also make it a crime for people to call for a terrorist attack, even if they don't make a specific threat, and empower Canada's spy agency to thwart attacks directly in a significant expansion of their powers.
Work on the law began in October after a gunman killed a soldier at Canada's national war memorial and then stormed Parliament.
The attack in Ottawa came two days after a man, said to be inspired by the Islamic State group, ran over two soldiers in a parking lot in Quebec, killing one and injuring the other before being shot to death.
Under current law it is a crime to make a specific threat. The new law will make it a crime for a person to call for terror attacks on Canada generally or to promote or advocate others to carry out terrorism elsewhere.
"We cannot tolerate this any more than we tolerate people that make jokes about bomb threats at airports," Harper said.
"Anyone engaging in that kind of activity is going to face the full force of the law in the future."
Harper said jihadists have declared war on Canada and it would be a grave mistake to ignore their threats.
"Over the last few years a great evil has been descending upon our world, an evil that has been growing more and more powerful, violent jihadism," Harper said.
Under the current law those suspected of being involved in a terror plot can be detained for up to three days. The new law extends that to seven days provided police get a judge's permission.
