The decision follows a trial in eight stores with any unsold baguettes and boules being prepared and filled with garlic butter at the end of each day.
The products were then sold as frozen with a shelf-life of 30 days.
The retailer plans for the scheme to be introduced to 200 M&S food outlets across the UK – the products will be sold in 100% recycled packaging.
Paul Willgoss, M&S Food Director of Technology, said: “By turning leftover loaves into frozen garlic bread, we’re not only creating delicious new products for family mealtimes, but we’re also helping to spark change together with our customers to significantly reduce waste.
“What’s more, they can now be confident that the packaging they take home from our bakeries will be recycled and given a new purpose too.”
The firm has set a goal to halve food waste by 2030.