The deal was struck by B&M’s subsidiary, EV Retail Limited, for £152 million.
Heron, which reported revenues of £274.4 million and pre-tax profit of £8.6 million for 2016, offers 1,200 stock-keeping units, including ambient and frozen food. It operates 251 stores, with an average 2,500sq ft of retail space compared to B&M's UK average of 19,000sq ft.
B&M has around 500 outlets.
The company said: "Convenience is one of the areas of growth in grocery retailing today, although much of this growth to date has been based on premium pricing. The Board of B&M believes that Heron’s expertise and attractive existing store portfolio, when supported by B&M’s proven sourcing, retailing and store roll-out capabilities, can bring an attractive new customer value proposition in an expanding sector of the grocery market."
B&M chief executive Simon Arora said: "B&M is already the UK's leading general merchandise discount retailer, serving four million shoppers per week. The addition of a complementary, proven discount convenience grocery brand to our own structural growth story gives the combined business an even longer, exciting growth runway. I look forward to working with David and Andrew Heuck and the Heron team to drive forward our shared ambition to deliver exceptional value for money to shoppers across the UK."