'Dallas' star Patrick Duffy joins St Patrick's Day celebrations in Ireland
The US actor, whose great-grandfather emigrated to the United States in the 1920s, helped kick off the festivities by blowing out the candles on a large green cake to mark his 74th birthday.
"The beauty of my feeling of being in this parade is the coming together of the heritage that I have, that I'm discovering on a daily basis by being here," said Duffy, who is this year's international guest of honour.
"Return is the key word that people feel when they come to Ireland, the sense is that you’re returning somewhere," he told reporters.
In Washington, Varadkar was due to meet US President Joe Biden for lunch later as part of his annual Washington visit to mark the Irish patron saint's day.
Biden is fiercely proud of his Irish roots.
Earlier Friday, Varadkar and his partner Matthew Barrett enjoyed a St Patrick's Day breakfast event hosted by Vice President Kamala Harris.
In addition to the Dublin parade, celebrations were due to take part across Ireland's towns and cities.
The Dublin parade featuring the traditional marching bands and pageants will only be the second since an enforced hiatus due to the Covid-19 pandemic.
As well as locals, the event is a major draw for international visitors, many of whom have Irish ancestry.
At the Cheltenham Festival -- an annual event for Irish horseracing fans, spectators got into the spirit, donning green outfits and shamrock sunglasses.
St Patrick is also a patron saint in Nigeria -- home to a stronger version of Ireland's famous Guinness stout.
Catherine, also known as the princess of Wales, took over Friday as the honorary colonel of the Irish Guards, replacing her husband.