The 57-year-old singer, who once declared she'd never re-marry, had a private ceremony in the presence of friends and family in a boat on the River Thames on Saturday, reported Express online.
A spokeswoman for the star has confirmed the nuptials, stating the couple wed "in a private ceremony with friends and family present".
Oscar winner Colin Firth was among the guests.
Lennox met Besser in 2009 at a fundraiser for his Mothers2Mothers AIDS charity - when the doctor was still married to his now ex-wife Debra.
Lennox's grown-up daughters Lola and Tali were among the bridesmaids at the wedding.
The star split from their father, record producer Uri Fruchtmann, in 2000. They were married for 12 years.
