The firms have worked together on a number of projects in the capital installing and maintaining sophisticated building controls systems on complex office buildings.
TClarke has paid £1.5m upfront for Eton with up to another £1.1m due in staged payments if future earnings targets are met.
For the year ended 31 May 2016 Eton reported revenues of £9.5m and a pre-tax profit of £300,000.
The deal will see around 80 Eton staff join TClarke at its Moorgate head office and prefabrication facility at Stansted.
Eton’s main current clients include Canary Wharf Management and Contractors, CBRE Maintenance, Lend Lease, Sir Robert McAlpine and Stanhope.
Mark Lawrence, CEO of TClarke said: “We welcome the Eton team to TClarke and I am confident that the business will reach new potential as part of a larger group enabling them to build upon the scale and number of projects undertaken.
“Increasingly, our clients are demanding ever more sophisticated systems to control their buildings. With this acquisition we are able to deliver a joined up ability to meet these demands.“
Jamie Ward, Managing Director of Eton added: “We are delighted to be joining TClarke.
“The Group has established an outstanding reputation within the industry for its first class approach to working with its clients on some of the most complex projects in the UK.
“We have always enjoyed working with them and by combining our expertise I am confident that the prospects for our clients and our staff will be greatly enhanced.”