The mum-of-three opted for burgundy Jimmy Choo stilettos and a matching clutch, along with earrings also from Erdem.
The young royals have been strong advocates for mental health, setting up the Heads Together campaign in 2016 through their official charity, The Royal Foundation.
eBay revealed that searches for tailored maternity coats more than tripled in November 2017, after Kate and Prince William announced they were expecting their third child, while searches for British designer Jenny Packham increased two-fold following Kate's appearance with newborn baby Louis outside of the Lindo Wing, wearing a red smock dress by Packham.
The summit sees political figures, academics and policy-makers from around the world meet to discuss issues surrounding the stigma of mental health and how to better address them.
During the event, William aimed a good-natured ribbing at his wife after Middleton, who studied art history at the University of St. Andrews in Scotland, added a brushstroke to artist Dairo Vargas' painting. At the summit, William and Kate visited a stand run by the non-profit organisation United for Global Mental Health, where they heard about the work of Dixon Chibanda, who started an initiative in Zimbabwe teaching elderly women the skills to offer therapy sessions on "friendship benches".
Last month Prince William opened up about the emotional toll of witnessing suffering during his time as an air ambulance pilot. This Friday, she will lead a number of senior royals at Princess Eugenie's lavish wedding at Windsor Castle, where George and Charlotte will feature in the tiny bridal party as pageboy and flowergirl.