Paul Barton is a senior solicitor in the department and is joining Field Fisher Waterhouse as a partner.
He says he has been leading the IT team at Simmons & Simmons and that he is credited with making the firm highly-regarded in the area.
Sources close to The Lawyer suggest that Barton could take both clients and assistants with him to Field Fisher Waterhouse.
Barton says: "I think both myself and others here are disappointed that Simmons & Simmons is not prepared to offer more resources and backing to the IT group.
"The fact that there is not a partner in the area goes to prove a lack of commitment. I am keen to move to a firm that is building up IT. I am pleased Field Fisher Waterhouse has identified IT and online law as one of its key areas," he adds.
A Simmons & Simmons spokeswoman tells The Lawyer that the IT group is part of the larger communications department and Barton was not the head of the group.
"We wish Paul well in his new job and he goes with our best wishes," she says.
The firm denies that it is not committed to IT work, saying: "IT is and will remain a significant part of our sizeable communications practice."
Barton is the second partner to join the practice at Field Fisher Waterhouse since June, when leading IT lawyer Nigel Wildish moved to join the firm from Osborne Clarke.
Barry Fishley has also been promoted to partner from within the department this month, bringing the number of partners to four.
Head of the group Michael Chissick says: "We are delighted to welcome Paul as a partner.
"He was effectively head of IT at Simmons & Simmons and, with his experience and expertise in the field of ecommerce, he will make an immediate and valuable contribution to the team."