Communications giant Avaya has closed its offices at Maidenhead Office Park.
The company took over Eton House at the site in Westacott Way following the £900m acquisition of Nortel, which went into administration in 2009.
Hundreds of staff lost their jobs as a result.
The acquisition came after Nortel's European headquarters had been in Maidenhead for more than 10 years.
Avaya continued to operate on the site with a reduced staff but due to the presence of an office less than 30 miles away in Guildford the decision was made to close.
A statement from the firm said: "Avaya is consolidating some locations from which it operates, including the Maidenhead offices, which were consolidated with the Guildford location at the end of December."
It added the organisation had worked with employees to ensure a 'smooth transition'.
The company was not prepared to comment on how many jobs would be lost as a result of the move.
Avaya took out an eight-year lease on Eton House and will be responsible for finding a new tenant.
The four other buildings on the site, all formerly occupied by Nortel, have organisations using them or set to arrive.
Bray House was leased to telecommunications company Genband, and a large part of Ascot House was taken by Quest Software once renovations were completed.
Research firm Covance relocated its offices from previous premises in Crawley and Foundation Park, Maidenhead, to the office park at the beginning of the year.
The final building is due to be taken by Toys 'R' Us in June.
Top Ten Articles
The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.