Speaking outside Wardhill Castle in Aberdeenshire, where the pair will exchange vows on Saturday, Sebastian Leslie said: "We are absolutely thrilled for Kit and Rose to be marrying today."
The local councillor added: "It's an absolutely lovely day for us."
The couple met while filming the fantasy saga in 2012 and played on-screen lovers Jon Snow and Ygritte.
The actors, both 31, are marrying in Leslie's 12th-century family castle on Saturday.
It is understood that over 80 members of the couple's family and close friends, including their GoT co-stars Emilia Clarke and Peter Dinklage, will gather for the celebration.
The couple will exchange their vows in the ornate drawing room of the castle, which can accommodate up to 80 witnesses.
A massive luxury marquee with six peaks has been erected to host the wedding reception, speeches and wedding breakfast.
Preparations were in full flow yesterday as florists, caterers and family members busily travelling along the narrow country lanes to the remote castle.
Small hand-painted signs are dotted around the grounds to make sure that guests don’t get lost.
A notice of the couple’s marriage was posted at the register office in the nearby town of Huntly.
It read: "Christopher [Kit] Catesby Harington is proposed to marry Rose Eleanor Arbuthnot Leslie on [Saturday] 23 June 2018, under entry number 317/2018/42 of the Huntly Register marriage notice book."
Kit recently revealed he asked producers to shut down filming on Game of Thrones final season so his castmates could attend their big day.
He said: "I rang up [the producer] and I said, 'I'm getting married and it's your fault actually'... I think for the final season he is so stressed that he's reached that peaceful level.”
“I was like, 'You need to factor in a Game of Thrones wedding by the way.' They have all got to be there so the whole thing has got to shut down."