Boris Johnson has promised the Integrated Review will modernise the Armed Forces for present threats.
However, he failed to give many details over future personnel numbers, as he repeatedly avoided questions about cuts through natural turnover.
In response to a question from Labour MP Nick Smith about reports that numbers of military personnel will be reduced, Mr Johnson stated: "There'll be no redundancies across the Armed Forces."
He later said: "The Army, including reserves... will be over 100,000.
"But it is the duty of this Government to take the tough decisions that are necessary to modernise our Armed Forces, as well," he added.
Earlier in the Commons session, Labour leader Sir Keir Starmer earlier warned that there is "a very real risk" the Armed Forces will be "stripped back even further", adding: "This review won't end the era of retreat, in fact, it will extend it."
The last defence review set a target size for the regular Army of 82,000 soldiers and just over 30,000 reservists, a total of about 112,000.
However, right now the number of Army regulars and reserves total just over 103,000, with the regular Army strength more than 5,600 people short and the Army reserve nearly 3,200 below trained strength.
The Prime Minister's new minimum of 100,000 could mean thousands of Army posts may disappear as people leave.
The services will be reconfigured to fight battles of the future with high-tech equipment, according to the Prime Minister.
However, he offered no details outlining what the modernisation will look like or how many people will be in the Armed Forces.
Regarding hardware, the newly-published report mentions a "new Multi-Role Ocean Surveillance Ship" for the Royal Navy, plus a pledge for the UK to have "at least 48 F-35s by 2025".
The Integrated Review also commits to Britain deploying "more of our Armed Forces overseas more often and for longer periods of time" for training and exercises.
The Prime Minister announced in November a £16.5bn increase in defence spending over the next four years, focusing on the future battlefields of space and cyber.
For more discussion on the Integrated Review, click through to this week’s episode of the Sitrep Podcast.