Dashing batsman Ponting, currently leading Australia in Sri Lanka, will be available for the final stages of the Twenty20 competition and the semi-final of the C and G Trophy, English cricket's domestic One-day knockout competition in July.
Ponting, recently named Australia's cricketer of the year, said in the statement, "I am really looking forward to my stint with Somerset and hope my new team mates will play well to qualify for the later stages of both cup competitions. "If they have played that well, I might not get in the team!"
Somerset also said they hoped to have Ponting available for four National Cricket (One-day) League games against Worcestershire, Sussex, Yorkshire and Durham.
The west Country club's statement added, "He will also play in four championship (England's first-class equivalent to Australia's Sheffield Shield) matches against Glamorgan and Hampshire at the County Ground and in the away matches against Durham and Yorkshire." The last of these takes place in August.
Somserset captain Mike Burns said of Ponting's impending arrival, "It will be terrific thrill to have him in the side and the rest of us have a big job to do ahead of his arrival. "It is a big incentive for everyone and I dont think that I will be hesitating over his selection!"
Ponting is not the first Australia captain to play for Somerset. Both Greg Chappell and Steve Waugh had spells at the Taunton-based County.
Meanwhile Somerset also announced that England fast bowler Andy Caddick had agreed a new four-year deal that would keep him at the County until the end of the 2007. New Zealand-born Caddick, 35, has only ever played County cricket for Somserset having made his debut for them back in 1991.
He missed most of the 2003 season with a back injury for which he underwent surgery in the autumn. But he recently resumed bowling and appears to be on course to reach his target of being fully fit for the start of the coming English season which starts in April.
Somserset chief executive Peter Anderson said, "It is fantastic news that Andy has agreed to sign a new deal with us. This is a typical example of his loyalty to the club especially when we know that other Counties were chasing him."
However, Caddick said it was a simple decision to stay put. "Somerset gave me my chance in the first place so why would I want to turn my back on them now?"