As bagpipers played traditional and pop tunes at Mons Barrack in Aldershot, Kate donned a gold shamrock brooch to top off her head-to-toe green as she took part in the annual parade.
Kate and William, (in his ceremonial Colonel of the Regiment uniform), looked tanned after their week-long break in the Maldives last week, and she decorated her forest green coat by Hobbs with the Cartier jewelry that was traditionally worn by the late Queen Mother.
Teaming her coat – which had its own flourish of shamrock – with a matching hat by Gina Foster, she stood alongside William on the dais as the ceremony to hand out the shamrock began.
The Duchess handed over baskets containing 300 sprigs of shamrock to the warrant officers for distribution among the guardsmen.
Next it was the officers' turn to get their emblem of the day. Finally, Kate pinned a sprig to 19-month-old Domhnall's red tunic. The dog's ceremonial jacket comes with Irish Guards' uniform brass buttons and a silver necklace.
The late Queen Mother, great grandmother to Prince William, traditionally undertook the ceremony to hand out shamrocks. Kate took on the role three years ago and has been joined by William for the day since he was made Colonel of the Regiment shortly before the couple's wedding in June 2011.
Kirsty Wigglesworth / AP