She offered her support to the Scotland Malawi Partnership's pledge after a report showed the link benefited around 1.3 million Malawians.
Ms Lennox was recently awarded the Barclays Woman of the Year for her work with HIV/AIDS and women in the developing world.
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Hide AdOther people who have signed the pledge include External Affairs Minister Fiona Hyslop and former First Minister Jack McConnell, who pioneered the friendship by signing the agreement with Malawian president Bingu wa Mutharika in 2005.
Marking the fifth anniversary of the agreement, a free trade exhibition at Our Dynamic Earth showcasing Malawian products will be open from 11.00am to 4.30pm.