The glowing royal, who is five months pregnant with the couple's first child, looked radiant as she stepped out in a floor-length silk maxi gown by Seraphine, a maternity brand that is popular with Kate Middleton. Zara was all smiles as she headed into the Grosvenor House Hotel for Saturday night's affair on Park Lane.
The accomplished horse rider completed her look with black high heels and a sparkly gold clutch, and pulled her blonde hair back in a low ponytail.
The Queen's granddaughter was joined by a host of famous royal faces at the lavish event, including her cousins Prince Harry and Princesses Beatrice and Eugenie.
Prince Harry looked dapper in a black tuxedo and arrived with his personal security guards, while his girlfriend Cressida Bonas was spotted riding in the same car as Princess Eugenie.
Princesses Beatrice and Eugenie attended the high-society bash with their boyfriends, Dave Clark and Jack Brooksbank respectively.
The elder of the sisters, Princess Beatrice, sparkled in a gold-sequined top and flowy cream skirt, while Princess Eugenie donned a floor-length black dress with beaded halter top.
Beatrice arrived hand in hand with Dave who looked dapper in a classic tuxedo. The couple were joined by their close friends and newlyweds Sam Branson, Richard Branson's son, and his wife Isabella Calthorpe for the evening.
Other celebrity guests in attendance included television personality and close friend of Zara, Natalie Pinkham, and singer Katherine Jenkins.
Pippa Middleton and her stockbroker boyfriend Nico Jackson also stole the spotlight as they arrived at the ball. The author and columnist showed off her glowing tan in a striking black and orange gown, which she paired with black peep toe heels and a matching clutch.
In the past, Pippa's sister Kate Middleton has turned heads at the Boodles Boxing Ball. Before her marriage to Prince William, Kate attended the ball twice — once in 2008 wearing a show-stopping pink gown and again in 2006 donning in a sky blue dress.