The stars were among the 14,000 participants swimming, cycling and sprinting through the capital this weekend in the largest event of its kind in the world.
Speaking before the triathlon, Hasselhoff commented: "I run in slow motion really well on Baywatch, but I've not competed before. But I'm ready."
Burke later said of the race: "It just brings people together. [The crowds] give you so much motivation, it just feels epic."
Explaining his motivation for holding the event, Branson said: "I think if you're fit and healthy you can achieve pretty well anything in life.
"If you let your body go it's very difficult to get up and go. I find it a very important rule in my life and it's worked for me."
Other celebrities taking part in the Virgin Active Triathlon included TOWIE's Lydia Bright, Waterloo Road actress Chelsee Healey, Gareth Gates and Nell McAndrew, who is currently three months pregnant.