Benali, 50, swam 12 miles, ran five marathons, cycled 560 miles and burned almost 61,000 calories during his mammoth challenge.
An emotional Benali, who ended up in hospital during one stage of the gruelling week, said: “There were some pretty tough days but this just puts the icing on the cake.
“I’m very, very pleased and emotional – it’s absolutely incredible.”
The challenge was his third and final in a bid to hit the £1m target in aid of Cancer Research UK.
He added: “It was the best news to wake up to this morning.
“I just can’t thank everyone enough that’s supported the challenges in some shape or form.
“It’s all about trying to bring a cure for this awful disease and find better treatments.”
He started the challenge in Manchester and finished in Southampton, his home city, where more than 1,000 people turned out to cheer him home.
Mr Benali chose to fundraise for the cancer charity as many of his family and friends have been affected by the horrible disease.
Michelle Mitchell, of Cancer Research UK, said: “I would like to congratulate and thank Franny for his phenomenal achievement.