The union said by throwing its weight behind the nationwide initiative to back British farmers, Lidl had underlined its commitment to working in a sustainable way with all of its growers.
Aldi is the only other supermarket to sign up to the pledge.
Lidl said it had worked closely with many of its growers for more than 15 years and that backing the promise highlighted its commitment to putting security for suppliers, fair terms, price certainty and elimination of waste top of the agenda.
The UK’s fastest growing supermarket also vowed to continue its on-going promotional activity with growers, including the ‘Pick of the Week’ promotions, specifically designed to provide flexibility yet security to their supply base through crop-availability-led planning.
Ali Capper, NFU horticulture and potatoes board chairman, said: “We are delighted that Lidl has publicly committed to our pledge, highlighting its commitment to long-term supply relationships, equitable distribution of reward along the supply chain, and fair and respectful trading relationships.
“Our goal is to generate integrity, honesty and openness across the market and that can only come from the key asks within our pledge – which includes price certainty, transparent working and strong, long term relationships that are fair for everyone involved.
"Lidl, with its already long history of working closely with its suppliers, is an ideal candidate to make the pledge.”
Ryan McDonnell, commercial director for Lidl UK, added: “We are very proud to have developed and maintained strong, long-standing relationships with all our suppliers, and our commitment to the NFU pledge cements this further. We’re also very keen to ensure that our sourcing process supports the growth and development of UK growers, which is vital in encouraging more and more people, particularly our shoppers, to regularly eat more fruit and veg.”