The move on Thursday came a day after Zelenskyy announced a state of emergency that allows authorities to impose restrictions on movement, block rallies, and ban political parties and organisations “in the interests of national security and public order”.
Al Jazeera takes a quick look at what the measure means and its implications for Ukrainians.
What is martial law?
In an address on Thursday, Zelenskyy said the measures were being taken in response to Russia’s act of aggression, urging people to not panic and remain at home.
“Dear Ukrainian citizens, this morning President Putin announced a special military operation in Donbas. Russia conducted strikes on our military infrastructure and our border guards. There were blasts heard in many cities of Ukraine,” Zelenskyy said in an address to the nation.
“We are introducing martial law on the whole territory of our country.”
The measure is usually accompanied by curfews, the suspension of civil law, and the application or extension of military law and justice to civilians.
What does this mean for ordinary civilians?
When martial law is invoked, military officials and not civilian leaders make and apply the law. This means that Ukrainian soldiers, not police, are responsible for enforcing laws.
As such, ordinary civilians could be tried in military tribunals as opposed to civilian courts if they are accused of breaching martial law.
How is it different from a state of emergency?
While similar, legal scholars say a state of emergency is limited in both scope and duration. This is because most modern-day constitutions have laid out the conditions under which the measure can be invoked.
In contrast, martial law is a more ambiguous concept that is subject to the interpretation of those who enact it.