Meghan opted fro an olive green Ralph Lauren dress, which featured a boatneck and a matching hat by Stephen Jones. She also carried matching olive green gloves and a clutch.
The Archbishop of Canterbury, Justin Welby, who officiated their royal wedding on May 19, also presided over the christening. Meghan shared a friendly laugh with Welby before she entered the chapel.
On Tuesday, the royal couple are heading to Dublin for their next big public appearance.
They will spend two days in the Irish capital, which will include a trip to Guinness Storehouse.
Harry and Meghan will also head to Australia, Fiji, the Kingdom of Tonga and New Zealand in the fall for their first royal tour as a married couple.