The study will focus on two areas: generic software such as management information systems; and outsourced services where private contractors build or manage IT infrastructure.
In 2012-13, the public sector spent £13.8bn on IT products and services.
Earlier this year, the OFT put out a call for information, and the responses highlighted high barriers to entry in the market, and high costs for public sector organisations when switching suppliers.
The OFT plans to complete its study and publish findings in March 2014.