The company, whose headcount has grown from eight to 23 in recent months, welcomed Royal Mail chief executive Moya Greene to the event at Lauriston Street. They were joined by Deputy First Minister John Swinney.
Earlier this year, Royal Mail led a £2.5 million funding round to help Mallzee scale up its mobile shopping app, which gives shoppers a single point of access to more than 150 retailers.
"We believe that we can continue to rapidly add significant value to the Mallzee business by introducing their solution to a wider audience," Greene said.
"Our investment also helps align Royal Mail with the rapid growth in consumer purchases made from mobile devices”.