A Delta outbreak which began in June has produced nearly 3,000 infections and led to nine deaths.
Australian Defence Force soldiers will undergo training on the weekend before beginning unarmed patrols on Monday.
The lockdown – in place until at least 28 August – bars people from leaving their home except for essential exercise, shopping, caregiving and other reasons.
Despite five weeks of lockdown, infections in the nation’s largest city continue to spread. Officials recorded 170 new cases on Friday.
State Police Minister David Elliott said it would help because a small minority of Sydneysiders thought “the rules didn’t apply to them”.
Information provided by health officials indicates the virus is mainly spreading through permitted movement.
The outbreak has largely affected critical workers and large family groups in the city’s poorer and ethnically diverse west and south-west suburbs. About two million people live there.
Critics say those areas have already faced “targeted” policing measures. They point out restrictions there are harsher than for the rest of Sydney.
“They can’t afford to pay the mortgage, the rent, the food or work. Now to throw out the army to enforce lockdown on the streets is going to be a huge issue to these people,” he told SBS.
Others have called for the government to increase its vaccine drive and support services for the affected communities.