The firm will invest US$40mln on a second distribution centre in the US as part of its international expansion plans.
The new warehouse, near Atlanta, Georgia will have space for 10mln items with operations due to begin in autumn next year.
ASOS is the UK’s most valuable online fashion retailer with a market cap of £5bn.
“This agreement is a major step forward for ASOS in the US and demonstrates the opportunity we believe lies ahead in this key market,” said chief executive Nick Beighton.
US sales account for 12% of the group’s total sales, growing at a faster pace than the UK.
The US division delivered a 38% increase in US sales in the first quarter to £94.4mln, compared to a 16% increase in its UK arm to £234.6mln.
A shift in consumer behaviour towards online shopping continue to support ASOS during the period, with overall retail sales up 38% to £889.2mln and pre-tax profit up 14% to £27.3mln.