According to Sky News, the investor, who already backs the online home furnishings firm Wayfair, will reportedly have to part ways with roughly £150m to complete the takeover.
Founded by Holly Tucker and Sophie Cornish in 2006, Notonthehighstreet acts as a marketplace for 5,000 small business-owners.
The firm operated over stagnant total revenues of £35m for FY 2019, as it served in excess of 2.5m customers.
The group has now been up for sale for several months after hiring bankers at Evercore to search for bidders.
While further interest has been gathered from potential investors, including the London-based private equity firm, Exponent, the advanced talks with Great Hill signal the closest negotiations have come to a deal so far.
Notonthehighstreet’s current financial backers include German publisher Hubert Burda Media, Index Ventures, and an arm of the asset management group Fidelity.