The chief sniper during the Lindt Cafe siege will sue NSW Police, alleging he and fellow officers were prevented from doing their jobs and the lives of cafe manager Tori Johnson and barrister Katrina Dawson could have been saved.

The officer, who can only be identified as Sierra 3-1, alleges in a 30-page affidavit he has suffered psychological trauma due to decisions taken by his superiors during the siege on December 15, 2014 in which 17 people were taken hostage.

The Daily Telegraph reports the civil action, lodged in the NSW District Court on April 12, will be heard next year in a one-day hearing.

It follows another complaint he made to the Law Enforcement Conduct Commissioner that was dismissed, that claimed senior officers perjured themselves at the initial inquest.