The deal is now conditional on the approval of Research Now's shareholders. The offer represents a 30% premium to Research Now's closing price of 330p on 4 September which was the last day before e-Rewards' made its offer. Its shares have risen since then to close at 420p.
Dallas-based e-Rewards is the world's largest "by invitation only" research panel which pays volunteers over the internet to test its clients' products.
Hal Brierley, chairman and CEO of e-Rewards, said: "The acquisition of Research Now by e-Rewards represents the coming together of two well regarded companies to form a significant global firm that will be well positioned to serve the international online fieldwork and online panel sample services needs of marketing decision makers and market researchers."
Research Now's chief executive, Chris Havemann, will stay on as chief executive of the new UK company.
He will also join the e-Rewards board along with Research Now's chairman Geoff Westmore. Shareholders will be asked to approve the management arrangements.
Westmore, chairman of Research Now, said: "Against the backdrop of a consolidating market, e-Rewards and Research Now are highly complementary companies and their combination is very exciting.
"Bringing together these two leading quality players in the online fieldwork market will create a unique global offering for our combined customer base."
In July Research Now reported a 24% increase in revenues to £23.6m for the first half of April 30.