Australian Prime Minister Tony Abbott has offered his sympathy to their families.
Tori Johnson, 34, was shot dead after he heroically tried to wrestle the gun from the hostage-taker inside the Lindt cafe in Martin Place just after 2am local time this morning.
Katrina Dawson, a 38-year-old mother of three young children, later died in hospital after being held hostage for more than 16 hours.
She was a barrister at Eight Selborne Chambers in Sydney's Phillip Street, opposite the Lindt cafe.
The NSW Bar Association paid tribute to the highly respected barrister.
"Katrina was one of our best and brightest barristers who will be greatly missed by her colleagues and friends of the NSW Bar," association president Jane Needham SC said in a statement.
"She was a devoted mother of three children and a valued member of her floor and of our community."
Ms Dawson, who attended prestigious girls school Ascham, topped the state in the Higher School Certificate in 1994 with a TER of 100. She also topped her bar exams and is the sister of well-known media barrister Sandy Dawson.
The gunman, self-described Muslim cleric Man Haron Monis, was also killed in the attack.
Hundreds of floral tributes have started to appear in Martin Place and the NSW Police Commissioner Andrew Scipione personally visited the site this morning.
How the siege unfolded (all times Sydney local time).
Monday, December 15
* 9.45am - A man walks into the Lindt Chocolat Cafe in Sydney's central business district reportedly carrying a sports bag containing a gun.
* 10.10am - Customers and workers are pressed up against the glass of a shop window inside the cafe.
* Martin Place shut down with scores of police surrounding the building.
* 11am - Parts of the CBD placed in lockdown, Sydney Opera House, State Library and court houses evacuated.
* Siege chaos causes major traffic disruptions: Martin Place train station shut down
* Prime Minister Tony Abbott offers NSW federal support to deal with the siege in Sydney's CBD.
* Lindt Australia CEO Steve Loane says he believed between 40 and 50 people, customers and employees, were being held hostage in the cafe.
* 3.30pm - Three men flee from the cafe and into the safety of heavily armed combat police.
* 4.30pm - Performances at Sydney's Opera House are cancelled.
* 4.55pm - NSW deputy police commissioner Catherine Burn says police are still trying to work out the gunman's motivation.
* 5pm - Two more people, females, flee the cafe.
* 5.45pm - The gunman reportedly demands delivery of an Islamic State flag and a conversation with Prime Minister Tony Abbott.
* 7pm - Mosques, synagogues and churches welcome worshippers, in what their leaders say is a show of community solidarity.
Tuesday, December 16
* 1am - Gunman identified as 50-year-old self-styled sheik Man Haron Monis.
* 2.14am - A group of hostages run from cafe.
* 2.17am - Two more men and two women race outside cafe.
* 2.20am - Ten seconds of rapid gunfire as heavily-armed police storm the cafe in numbers, managing to release others, a woman carried from the scene injured.
* 2.25am - A second volley of shots erupt before the cafe fills with police and paramedics.
* 2.51am - Reports of two fatalities
* 5am - The gunman said to be one of the dead.
* 5.29am - Three people injured following the siege - a woman in her 40s with a gunshot wound to the leg, a male police officer, 39, receives a "gunshot graze" to the cheek and a woman in her 30s was being treated for back pain.
* 5.38am - Three people confirmed dead, including the gunman. A 34-year-old man and a 38-year-old woman are pronounced dead after being taken to hospital. Plus the 50-year-old gunman.
* 5.55am - Police Commissioner Andrew Scipione confirms 17 hostages were held by the gunman.
* 6am - Prime Minister Tony Abbott commends the courage and professionalism of NSW police and other emergency services involved in the Sydney cafe siege.
