The gold medallist and six-time world champion powered to victory with the Light Blues in a feat dubbed “off the scale” by his former Great Britain colleague Matthew Pinsent.
Eight years older than the previous record-holder, Cambridge’s 1992 cox Andy Probert, Cracknell suffered a traumatic brain injury in 2010 after fracturing his skull in a bike accident.
But after last week confirming the end of his marriage to Beverley Turner, the Peterhouse College masters student pulled off an extraordinary personal achievement.
Cracknell conceded more than 25 years on some of his team-mates, but belied his age to leave friends and former colleagues in awe.
“This is the start of another chapter in his life,” friend and broadcaster Ben Fogle told the BBC.
“I think James wants this to be his flag, he wants this to be the moment that people say ‘James aged 46 did something most people doubted’.”
Cracknell’s fellow former Olympian Pinsent added: “It’s extraordinary that he’s got himself into the shape, at 46, of a 24-year-old. I only know one person who could do that, and it’s James. It’s just off the scale.”
Cracknell’s life was turned upside down when he fractured his skull in a cycling accident in Arizona nine years ago but he battled back to top form and fitness.
“On the start I thought ‘I’ve missed this’,” Cracknell said after his victory.
“The first few minutes were great, but they just didn’t drop. To be honest the endurance wasn’t a problem.
“If I had any doubt it would have been my sprinting. I just made sure I stuck it in and hopefully we had enough in the bank.”
Cambridge also won the Women’s Boat Race for the third year in a row, beating Oxford by five lengths.
The Light Blues cemented their dominance over their traditional rivals, with new coach Robert Weber’s team storming into an early lead and refusing to relent. Cambridge stroke Lily Lindsay has rowed internationally for the US, but insisted nothing compared to a Boat Race victory.