She took the royal salute at the ceremony as the Prince of Wales and the Duchess of Cornwall, the Duke of Cambridge and the Duke and Duchess of Sussex watched nearby.
The Duke and Duchess of Sussex have received a warm welcome as they carry out a second day of engagements in Dublin.
Meghan Markle can be seen in the video above crossing her legs.
The royal couple arrived in the capital on Tuesday for their two-day visit to the country.
Kate and William don't often engage in public shows of affection (unlike their newlywed counterpart Meghan and Harry), so it's nice to see them sharing an intimate moment in the very place their royal love story began.
Meghan replied: "I'll come back and look out for the first female bust".
Markle's third outfit choice was the Emilia Wickstead dress which she wore with simple black heels to the garden party reception at the British Ambassador's residence in Dublin.
Earlier today, the Duchess of Sussex and Duchess of Cambridge attended a special service at Westminster Abbey to mark 100 years of the Royal Air Force.
For a touch of "Markle Sparkle", she showcased loose curls (after having worn her locks in a slick side bun throughout the day) and donned earrings by her go-to Canadian jeweller, Birks.
For 100 years the RAF has defended the skies of Britain, preventing conflicts, delivering aid and combating cyber threats while working in partnership with other services.
Following the service the family gathered on the balcony at Buckingham Palace for an impressive aerial display, with the Queen giving a speech commemorating the merging of the Royal Flying Corps and the Royal Naval Air Service on April 1, 1918.
The couple met RAF servicemen and women, charity representatives involved in the RAF100 Appeal, RAF Veterans and Civil Service personnel involved in the Centenary celebrations.
After arriving at Dublin City Airport, Harry and Meghan were due to meet with Irish Prime Minister Leo Varadkar.