People holding candles and torches observed a minute's silence at the start of the main event in Copenhagen.
Two people were killed and five police were injured in attacks on a free speech debate and a synagogue.
The gunman was later shot dead by police. He did not appear to be part of a wider terror cell, Denmark's PM said.
Earlier on Monday, two men were charged with providing and disposing of the weapon used in the attacks and helping the gunman to hide.