E-commerce spending increased 14% to $56.8bn, making it the first quarter to have crossed the $50bn mark.
The rise in spending during the quarter was driven by a 6% rise in the number of buyers and an 8% increase in spending per buyer.
comScore chairman, Gian Fulgoni, said f e-commerce continued to grow strongly, despite an uneven macroeconomic environment which is showing signs of recovery but still an area of concern.
"With e-commerce growth rates consistently in the mid-teens throughout the year, it is clear that the online channel has won over the American consumer and will increasingly be relied upon to deliver on the dimensions of lower price, convenience and selection," Fulgoni said.
"The only real blemish on an otherwise outstanding year for e-commerce was a holiday season that fell shy of initial expectations, apparently due to consumers’ fiscal cliff concerns.
"To the extent that this pullback was just a temporary shock and not a sign of underlying economic weakness, we are optimistic that 2013 will build on the momentum of the past year," Fulgoni added.
Online product categories grew about 15% compared to the previous year which include digital content and subscriptions, consumer electronics, toys and hobbies, apparel, accessories, books and magazines.
US retail e-commerce spending accounted for 10% of total retail spending in the country.