帕特里克-桑德斯爵士將軍將說，他從未見過 "像普京總統的野蠻侵略 "這樣明確的威脅。
He will give a speech on Tuesday - but has reportedly already asked the prime minister to increase defence spending to 2.5% of GDP by 2028.
The UK is currently spending around 2% of GDP on defence, matching the target set by the Nato for member nations.
Mr Wallace tell a conference organised by the Royal United Services Institute think tank that, in light of Russia's invasion of Ukraine, the threat has changed and governments must be prepared to invest more to keep people safe.
Defence sources have told the BBC's defence correspondent Jonathan Beale that Mr Wallace he wants an increase in the defence budget by the middle of this decade.
In a letter to Prime Minister Boris Johnson, the defence secretary also urged the PM to call on other Nato leaders to raise the spend per country to 2.5% of national income, Talk TV repots.
In response to questions about the letter's contents, a defence source told the PA Media news agency that the Ministry of Defence does not comment on leaks.
"The defence secretary and the prime minister have always said that the government will respond to any changes in threat which is why in 2020 the Ministry of Defence received a record defence settlement," the source said.
The worsening security situation for the UK will also be highlighted by the new head of the armed forces in his first major speech.
General Sir Patrick Sanders will say he has never known such a clear threat "as the brutal aggression of President Putin".
He is set to liken the war in Ukraine to the build up to World War Two, describing the Russian invasion of Ukraine as a "1937 moment" for the UK.
The speeches come ahead of a summit of Nato leaders in Madrid, which is also expected to address allies readiness and spending on defence.
The defensive alliance's secretary general Jens Stoltenberg has already made clear he wants a target of members spending 2% of their annual national income on defence to be a base line, rather than a ceiling.