The monarch, 95, held virtual audiences at Windsor Castle via video-link on Tuesday.
It is the first time she has been seen undertaking her royal duties since Philip, 99, died peacefully at the Berkshire royal residence on April 9.
The Queen no longer in a black mourning outfit, was dressed in a pale blue floral dress which featured large purple, white and yellow flowers, with a three-string pearl necklace and a diamond brooch as accessories.
She was pictured on a computer screen smiling as she held two audiences with the ambassador from the Republic of Latvia, and the ambassador from the Republic of Cote d’Ivoire, who were at Buckingham Palace.
Two weeks of royal mourning in memory of the Queen’s husband of 73 years ended for the monarchy and their households on Friday April 23, meaning the Windsors were allowed to go back to work full-time.
The royal family gathered for a poignant final farewell to Philip on April 17 at a socially-distanced funeral service in St George’s Chapel, with the Queen pictured sat alone as she grieved for her consort.
The monarch – who is the nation’s longest-reigning monarch – was back at work just four days after Philip’s death.
She held her first in-person event on April 13 – an audience and investiture with Earl Peel, who was relinquishing his role as Lord Chamberlain.
A day later she welcomed her new Lord Chamberlain, Baron Parker, who was overseeing Philip’s funeral, at another Windsor ceremony.
She was not photographed at these two events.
Although the Queen was not seen out and about in public, Buckingham Palace considers audiences official public engagements because they are listed in the court circular.
The Queen turned 95 just 12 days after the duke died and used her birthday to release a message thanking well-wishers for their tribute to Philip.
She said she and her family were in a “period of great sadness” but were comforted by words of praise for the duke.
“We have been deeply touched and continue to be reminded that Philip had such an extraordinary impact on countless people throughout his life,” she added.
Ivita Burmistre, ambassador from the Republic of Latvia, presented the Letters of Recall of her predecessor and her own Letters of Credence at the audience, as did Sara Affoue Amani, ambassador from the Republic of Cote d’Ivoire.