The 140 soldiers will reinforce 650 heavily armed men already on the ground and be followed by 1300 more next month, military spokesperson Brian Hillier said, making this mission Canada's largest and most dangerous abroad.
The force will regroup in Kandahar, in southern Afghanistan, where remnants of Taliban fighters and al-Qaida still hold sway.
Canada recently relocated its base to Kandahar from the capital, Kabul, taking over from American coalition forces, under the International Security Assistance Force (ISAF) banner.
They are tasked with imposing security, hunting down al-Qaida, and helping to rebuild the country that was devastated by two invasions; the Soviet invaded Afghanistan in 1979 and the US in 2001.
The deployment comes as Afghan fighters stepped up their attacks on foreign military targets in their country.
A senior Canadian diplomat was killed and three soldiers seriously injured last Sunday in a car bombing near Kandahar that also killed two Afghan civilians and hurt dozens more.
Diplomat Glyn Berry, 59, was the top Canadian political official in the region, part of the provincial reconstruction team. He died on his way to meet with a local Afghan leader, officials said.
Pressure is also mounting on the Netherlands to commit troops to southern Afghanistan and clear the way for Nato to improve the weak central government's influence in the region.
Days ahead of a major donors conference for the country in London, the military alliance's plans to broaden its toe-hold in the region to about 6000 troops are on-hold until the Dutch parliament endorses the move.
Nato wants to set its International Security Assistance Force (ISAF), which comprises about 10,000 soldiers from more than 30 countries, in the area alongside US forces in the middle of the year.
But Britain's role is in doubt until the Dutch commit, non-alliance country Australia is waiting to mobilise and Canada is going ahead with its own plans.
The Dutch government wants to send 1100 troops to Uruzgan province - one of Afghanistan's most dangerous - and keenly sought attack helicopters but it wants the endorsement of the parliament, which is largely opposed.
The head of the Dutch military will address the assembly late this month as the donor conference gets under way, and the government and parliament will hold a joint sitting on 2 February. But no date is set for a decision.
Britain, which has 8000 troops deployed in Iraq, would struggle to send more than the 900 extra troops destined for Afghanistan if the assembly vetoes.