The 96,000 sq ft centre in Enfield would help it "significantly increase" its share of north London online grocery, which it estimated as under 5%.
Most Asdas deliver between 10am and 10pm but Enfield will deliver from 7am till 11pm within a 45-minute radius. The centre had 50 delivery vans with the potential to double that in the next 18 months, Asda said.
Asda's first online picking centre in Morley opened last August and a third online-only store is set to open later this year.
Online is seen by Asda as a key to its plan to become the "clear number two" in food. "Online growth in food is almost as important as new space," executive development director Doug Gurr told Walmart investors in April. Last year Asda's online food sales grew 40% to £500m.