The 43rd president was speaking at an event on elections at the presidential centre in Dallas.
“In contrast, Russian elections were rigged. Political opponents imprisoned or otherwise are eliminated from participating in the electoral process. The result is an absence of checks and balances in Russia,” the former president said in his address.
“And the decision of one man to launch a wholly unjustified and brutal invasion of Iraq... I mean of Ukraine,” he added, before laughing it off and blaming his age for the faux pas.
He shrugged and said ”Iraq, too” under his breath. “Anyway. I’m 75,” the Republican leader added as the crowd erupted in laughter.
During Mr Bush’s presidency in March 2003, a US-led coalition invaded Iraq to overthrow the authoritarian government of Saddam Hussein over concerns about him acquiring biological and nuclear weapons, without showing evidence for the concerns.
The war, however, ended up bringing more conflict to the region.
His administration has been criticised for launching a brutal preemptive war on Iraq that killed tens and thousands of Iraqi citizens and over 4,000 US troops.
A study by Iraq Body Count pegged the civilian casualties from the invasion between 2003 and 2013 to be at 122,438.
Wednesday’s remarks were Mr Bush’s first public condemnation of the Russian invasion of Ukraine, nearly three months after it began.
Mr Bush faced heavy backlash for his Freudian slip.
“George W Bush is a war criminal,” senator Nina Turner wrote.
“Took 20 years for George W Bush to finally confess,” tweeted columnist Wajahat Ali.
Mr Bush also described war-time president Volodymyr Zelensky as a “cool little guy” and compared him to former British prime minister Winston Churchill, The Dallas Morning News reported.
“The way countries conduct elections is indicative of how their leaders treat their own people, and how nations behave toward other nations,” Mr Bush said.
“And nowhere is this on display more clearly than Ukraine.”
Meanwhile, as the war dragged on, the Ukrainian president has submitted a bill to parliament to extend martial law and military conscription by three months.
The law was first imposed on 24 February when Mr Putin declared “a special operation” in Ukraine. It has since been extended for 30 days on two occasions, with the latest extension set to expire on 25 May.