Shares in the e-commerce giant rose nearly 2 percent to a high of $US2,050.50 in morning trade before slipping back.
Apple reached the same milestone in early August.
Founded in 1994, Amazon is now the world's largest online retailer. Its chief executive, Jeff Bezos, is the world's richest man, with a net worth of more than $US160bn.
Neil Saunders, managing director of GlobalData Retail, said: "To reach a market capitalisation of over $1t is impressive. To do it in a little over 24 years is extraordinary.
"That Amazon has achieved this demonstrates its dramatic advancement in both the retail and technology sectors, as well as the influence it now wields over large parts of the consumer landscape."
Amazon reported nearly $US53b in sales in the three months ended in June, with record quarterly profit of $US2.5b.
The firm is expected to account for roughly half of all online shopping sales in the US this year - and nearly 5 percent of the country's overall retail market, according to research firm eMarketer.
It employs more than 575,000 people, a force nearly the size of Luxembourg's population.
It provides logistics, storage, loans and a selling platform to hundreds of thousands of third-party merchants.
Its profitable cloud computing division, which hosts huge swathes of the corporate world on its data servers, is the industry's global leader.