Communications Minister Malcolm Turnbull has made an impassioned plea for Australians not to be "corrupted by hatred" following the Lindt cafe siege.

An emotional Mr Turnbull was speaking after a memorial service held at Sydney's St Mary's Cathedral on Tuesday afternoon to pay tribute to the siege victims.

Lindt cafe manager Tori Johnson and barrister Katrina Dawson died after being held hostage for most of Monday in the Lindt Cafe in Martin Place. The gunman, Man Haron Monis, also died.

"I was on a train this morning, and you could feel the numbness in the carriage," Mr Turnbull said.

"Everyone was thinking the same thoughts: shock, horror, imagining how those people suffered during that terrible night.

"Thinking about the courage of the two young people that were killed.

"And yet I feel that everyone was also filled with love. There were something of determination on that train; a determined love; a recognition that it's love for each other, it's love for our country which binds us together and makes us the most successful, harmonious society in the world.

"I felt that there was, as the train rattled across the Harbour Bridge, I felt that there was a quiet determination that we weren't going to be intimidated by such hatred."

Tuesday's memorial service was led by the new Catholic Archbishop of Sydney, Anthony Fisher, and attended by NSW Premier Mike Baird and Governor-General Peter Cosgrove.

"I thought today's service was so beautiful," Mr Turnbull continued.

"Because it was all about love. It was about that love, that love of God ... the loving example of Jesus that should inspire us all not to be corrupted by hatred and violence, and to remain united as Australians, now and forever."

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