Jenkins and Judd joined more than 35,000 runners who took part in the 26-mile (42-kilometre) run through the U.K. capital, which kicked off with a 30-second silence in honour of those killed and injured at the Boston Marathon on Monday (15Apr13).
The stars also donned black ribbons in a show of solidarity for the Boston victims.
In a post on her Twitter.com page before the race, Jenkins wrote, "Happy Marathon Day!! We're awake & nervous but excited!"
British royal Prince Harry also turned up to present medals to the top runners, telling reporters, "It's a great opportunity for people from all walks of life to come along and raise money for their own personal charities, small or big. We're hugely fortunate for what the marathon does for us so I will continue to show my support where I can."
Earlier this week (15Apr13), three people died and more than 175 were injured when two huge blasts ripped through a crowd of spectators near the finish line of Massachusetts' Boston Marathon, but organisers of the British version vowed to press on with the London event.