Mr Wallace confirmed his departure – announced last month – in an exchange of letters with the PM.
Armed Forces Minister James Heappey and Chief Secretary to the Treasury John Glen have both been linked with the role.
However, there is also speculation about a surprise choice – with former defence secretary Liam Fox among the names mooted.
The changes to the government today are expected to be limited, after Mr Sunak backed away from a major overhaul.
Rishi Sunak is preparing for a mini-shuffle today after Ben Wallace formally quit as Defence Secretary
Mr Wallace confirmed his departure – announced last month – in an exchange of letters with the PM
Dr Fox, who served in the role under prime minister David Cameron between 2010 and 2011, was forced to resign after allowing his friend and best man Adam Werritty to take on an unofficial and undeclared role as his adviser.
The senior Tory MP backed Mr Sunak in last summer’s Conservative leadership race.
Mr Wallace, who served under three prime ministers in his current role, played a key role in the UK’s response to Russia’s invasion of Ukraine and was a close ally of Boris Johnson.
Seen as popular among Tory members, he was at one time seen as a potential leadership contender.
He ruled himself out of the running for the Conservative leadership last year despite being an early frontrunner in the race to replace Mr Johnson.
His successor will take on the high-profile role as the war in Ukraine continues
Mr Wallace wrote that he hoped the MoD was on the path to being ‘world class’ again
Source: | This article originally belongs to Dailymail.co.uk