The footballer - who already has three sons, Brooklyn, 12, Romeo, 8 and 6-year-old Cruz, with wife Victoria - insisted that he's "so lucky" to have a little girl.
In a video on his Facebook page, he said: "To have another girl in the family is really incredible. We've got three beautiful, healthy boys already and we're so lucky to have that and now to have a beautiful little girl, it's amazing.
"Having a daughter is a whole new thing. Having pink in the house and lilac in the house. And you have to be a lot more delicate with girls than with boys, and I'm not used to that, so it's a whole new experience but it's an amazing experience. To have that little bundle of joy in your hands, and her making her little noises and opening her eyes - it really is an incredible moment for us."
Beckham - who wore the number seven on the back of his shirt while playing for Manchester United and England - also explained the reasons behind Harper's name.
He commented: "A lot of thought goes into our children's names and Harper was a name we've loved for a long time for a couple of reasons.
"One of them was because Harper is an old English name which we loved and one of the other reasons is because Victoria's favourite book is To Kill a Mockingbird and the author was Harper Lee. And it's a very strong, passionate book, so that's where Harper came from.
"And Seven is partly because of the shirt number I wore for many years because I had so much luck around wearing that number, and it was such an influential number throughout my career and a lucky number, but that wasn't the main reason. The reason behind Seven is that it symbolises spiritual perfection and is a lucky number around the world. We love the name. We love Harper Seven and we're very proud of having her in our family."
Victoria recently tweeted that Harper Seven is "the most beautiful baby girl" she has ever seen.