A back injury had ruled the batsman out of the recent ICC Champions Trophy and had resulted in speculation that he could miss the upcoming Ashes.
However, having taken part in a training session earlier today, the 32-year-old will now feature for the first time since the Aussies arrived in England.
"Michael's playing. It's great news - his first game on tour and the Australian captain's pretty excited to play," said vice-captain Brad Haddin. "He's in a good spot. He had a bit of a hit in the nets today."
Australia team to face Somerset: Clarke, Haddin, Watson, Hughes, Cowan, Khawaja, Faulkner, Siddle, Starc, Pattinson, Lyon