Set up by Norton and Graham Stuart 12 years ago, So Television produces comedy and entertainment shows, including The Graham Norton Show and The Sarah Millican Television Programme.
ITV's production arm ITV Studios has agreed to make an upfront cash payment of £10 million to buy the company, with a further cash payment based on its profit performance up to July 31, 2016. The maximum value of the deal is £17m.
"So TV has been our baby for 12 years, so I'm thrilled that the ITV family has decided to take it under their wing and help it blossom," said Norton.
Graham Stuart added: "We are incredibly excited to be starting a new chapter in the So story with ITV Studios.
"Now we have the chance to achieve what we've always wanted to in this industry but with real strength and inspiration behind us."
ITV said that the acquisition fits with the key objective of the five-year transformation plan imposed by its new chief executive Adam Crozier when he joined the commercial broadcaster in 2010.
This objective was to "create world class content for multiple platforms, free and pay, both in the UK and internationally".
Following its successful debut on BBC Two this spring, The Sarah Millican Television Programme has been recommissioned for a second run, which kicks off with a Christmas special.
So Television also produces panel show Alexander Armstrong's Big Ask for Dave, which was recommissioned by the digital channel earlier this year.
ITV Studios managing director Denis O'Donoghue said: "So Television is known for its creative rigour and intense quality-control across its programming, whether that is its crown jewel, The Graham Norton Show, or its newer but no less brilliant The Sarah Millican Television Programme.
"Its programming presence on other channels is strategically terrific for ITV Studios, which has increased its output this year with new shows across the BBC, Channel 4 and Sky.
Kevin Lygo, who joined ITV Studios as its managing director from Channel 4, added: "So Television and Graham Norton have been making high quality programmes for many years now.
"I believe that ITV Studios can bring scale to their ambitions and together we can continue to keep The Graham Norton Show at the top of its game and increase the amount of new programming in their production slate.
"This is an important acquisition for ITV Studios and demonstrates our strategy to increase our capability in the production of high quality television entertainment programming."