H&M said it everything that is available in its high street stores will also be sold online.
The online store, which was initially planned to open in 2012, will also feature some clothes that are exclusive to Internet customers and the company's home decor collection H&M Home.
Daniel Kulle, U.S. President for H&M, said he was "thrilled to launch online shopping in the U.S."
"This significant milestone fully rounds out H&M's multichannel offering," he said.
H&M's 268 stores in the U.S. brought in revenues of 3.3 billion Swedish kronor ($503 million) in the second quarter, an increase of 2 percent compared to the same quarter a year ago.
The company's online store has previously only been available in eight European countries.
Chief executive officer Karl-Johan Persson earlier this month said he sees "great potential in the growing online market" and that the global rollout of the online store will continue in 2014.For more information visit: www.hm.com/us/shop-online-opening-us