The company has opened up an additional floor of the venue, offering space for up to 300 delegates theatre-style.
Dexter House, which opened in 2007, has consistently grown its business year-on-year and therefore decided to expand its space, according to Etc Venues head of business development Brendon Smith.
He said: "Dexter House has been a great asset, particularly as it's a London location with a garden setting. This new investment has created a space with great views and lots of natural daylight, and will ensure that the venue continues to grow."
The new suite at Dexter House is due to open in February.