Will.i.am, 37, looked at ease in the warm weather as he jogged through the Somerset town centre.
The Black Eyed Peas star's torch was "kissed" by that held by 26-year-old tae kwon do instructor Chloe Lock, from Honiton, Devon, to light the flame.
Before he started running he was passed his mobile phone and was tweeting as he set off down the road under Union Flag bunting. He also turned around to perform a short moonwalk to the delight of onlookers.
Speaking after his run, the music star said: "That was like a surreal moment. "I got a little more nervous this time than all the things I have done."
Will.i.am said he had known he would be in the torch relay for almost a year, but was told to keep quiet.
His moonwalk was in honour of his friend Michael Jackson: "Me and Mike were really close and he would have been proud that I ran the torch, so I thought why not moonwalk it a couple of steps while running with the torch."
The star turned and waved and thanked everyone for their support and said he would not be selling his torch on eBay, like some torchbearers have done.
"In my house the decor is gold and brown, so this is going to sit right on my wall," he said.