The live stream will be broadcast on the M&S Facebook page and will allow the public to ask Lumley questions in real-time by commenting below the video.
M&S claims that since launching the Shwopping scheme six weeks ago it has donated half a million used and unwanted items, equivalent to eight items a minute, to Oxfam for re-sale, re-use or recycling.
The retailer is asking its customers to exchange unwanted items of clothing of any brand when buying a new garment of clothing in its stores.
Lumley was hired by M&S to front the campaign, which falls under the brand’s Plan A corporate social responsibility drive.
M&S will attempt to reach a million "shwopped" items before the campaign hits the two month mark with a money-off event in stores this weekend, which will give away a £5 voucher to customers who "shwop" when spending £35 or more in-store.
Today's live video chat with 'Absolutely Fabulous' star Lumley will last for 30 minutes and begin at 12.30pm.
The retailer has also surveyed 2,200 consumers via YouGov about their recycling habits, which found one in five people have thrown away an item after wearing it just once.
Follow Matthew Chapman at @mattchapmanUK