The decorative body art was painted on Sophie's hand and index finger on Sunday by artist Humaira Rehrel, at the Heart and Soul garden party held by the Church of Scotland in Edinburgh.
Sophie, 49, was visibly thrilled at experiencing the ritual, which is traditionally carried out before Hindu and Muslim weddings.
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Sophie Wessex at the Heart and Soul garden party in Edinburgh
She was pictured beaming at the annual event celebrating global religion as the Pakistani artist applied the temporary ink, which lasts about three weeks.
Her husband of almost 15 years, meanwhile, was helping to prepare world cuisine in the kitchen nearby.
Henna derives from the plant which produces the reddish-brown paste used for tattoos, which represent health and good luck in the Arab world and India.
No doubt the bridal art had Sophie thinking back to her royal wedding, which took place just one month short of 15 years ago. She captured the world's attention on her big day at Windsor Castle in 1999.
The glowing bride wore an elegant, white hand-dyed silk organza dress, complementing her understated gown with a diamond tiara from the Queen's private collection.
Sophie has a close relationship with her mother-in-law the Queen. The two women share a passion for military history and a love of horses and are often spotted riding together at weekends in the magnificent grounds of Windsor Park.
Before taking on royal duties, Sophie worked in public relations, including four years at Capital Radio.
The Countess met Prince Edward at a charity event in 1993, with the couple dating for six years until they announced their engagement in January 1999 and married six months later.