The project will provide learning opportunities for disadvantaged young people through the Prince's Trust.
The enterprising farmers were brought together by Agrisgôp, a management development programme for farmers and their families run by the Welsh Assembly Government.
The farmers will supply 17 M&S stores with 200 lambs per week over six months. In return, the retailer is promising to pay a premium fixed price throughout the contract period, rather than a fluctuating weekly rate.
At the same time and as part of the project, the group of farmers will provide work placements for nine young people aged between 16 and 25 from the Prince's Trust, who will also attend their local agricultural college, Gelli Aur, in the hope they can successfully pursue a career in agriculture.
M&S will be promoting this initiative in-store, from 4 July through the use of the Prince's feathers on packs of lamb, along with words 'Working in partnership with the Prince's Trust Cymru to provide a sustainable future for young people in Wales'.