The prime minister released draft terms of reference for consultation on Monday, with a tentative starting time of July.
"We want this to be comprehensive," he told reporters in Sydney.
"Every single day the service of our veterans is something that is pressed on my mind."
Mr Morrison remains committed to establishing a permanent commission of inquiry into veteran suicides. But the independent office will operate alongside a standalone inquiry, which will take between 18 months and two years to deliver a final report.
The prime minister said governments made difficult decisions to deploy soldiers into war zones, but also needed to consider what happened to soldiers when they returned home.
"There is a far greater cost that is borne beyond those deployments, and that is the mental toll taken on the veterans after they return," he said.
"That cost is most significant when we see it in the death by suicide of our veterans."
The announcement comes just days after Mr Morrison confirmed the last remaining Australian troops would leave Afghanistan by September, in line with a timetable set by the United States.
The prime minister has previously rejected calls for a royal commission to be established, preferring his permanent model. But he was dragged into action after members of his own backbench threatened to cross the floor in support of a royal commission.
Julie-Ann Finney, who led the royal commission campaign after losing her veteran son to suicide, welcomed the announcement.
"Today is a long time coming for veterans and their families," she said.
"Finally, the voices of veterans will be heard. Finally, families can stand up and share their stories."
Ms Finney's petition for a royal commission has been signed by more than 409,000 people.
Labor has been calling for a royal commission into veteran suicides since December 2019.
"It is a tragedy that we've seen so many deaths as a result of veterans self-harming and suiciding since seeing active service and involvement in the ADF," Labor frontbencher Brendan O'Connor told reporters in Melbourne.
"It is certainly therefore welcome that the prime minister, belatedly, has chosen to make this decision."
Independent senator Jacqui Lambie called for such an inquiry in her first parliamentary speech in September 2014.
Today's the end of a fight, and the start of a whole new one.
The inquiry will examine all aspects of ADF service and the experience of those who transition to civilian life.
It will look at the availability and quality of health and support services as well as issues facing ADF members and veterans including family breakdowns, housing and employment.
Private sessions will be available for witnesses.
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