The scheme is dubbed the M&S and Oxfam Clothes Exchange and bills itself as the biggest clothing recycling campaign in the UK.
The vouchers will last for a month and can be used on purchases of £35 and above for people buying clothing, homewares or beauty products at M&S. The programme is being run on a trial basis for six months, starting from January 28.
The clothes donated can date back indefinitely, but the vouchers will not be available to people donating M&S most commonly sold items -- underwear and socks.
Sir Stuart Rose, chief executive of Marks & Spencer, said: "We are pleased that we have teamed up with Oxfam, the UK's biggest charity shop to help customers to raise money for developing countries by recycling their clothes they no longer need. It's a triple win -- it's good for customers, good for people in developing countries and good for the environment."