Established in 1984, the brokerage was owned and managed by Chris Steel.
All its existing employees will shortly move to larger, fully refurbished premises in Eastbourne town centre which will be branded as Equity Insurance Brokers.
Mr Steel said, "The support from Equity will allow this business to grow far more rapidly than expected. It will also ensure, particularly in an increasingly competitive market, it sustains the quality service the personal lines and commercial clients have come to expect."
Equity Insurance Group is based in Brentwood, Essex and its national network comprises more than 90 branches, four regional offices and two UK-based customer contact centres.
Mike Hutton, Equity's acquisitions director said, "Steel & Co Insurance Brokers fits our acquisition criteria of well-established town centre-based broking businesses along the south coast, a region where the group is strengthening its presence and actively seeking similar opportunities."