In November last year, it was announced that Mackintosh and her husband Hugo Taylor were expecting their first child together.
The pair, who were both original cast members on reality television series Made in Chelsea, were married in July 2018.
Just under two years later, Mackintosh has shared a first glimpse at their baby daughter, who was born a month ago.
The 30-year-old posted a black and white photograph of the family of three on Instagram.
In the picture, Mackintosh is wearing a long floral dress, while 33-year-old Taylor is wearing a loosely buttoned shirt and baggy shorts.
Their daughter, who is turned away from the camera, is wearing a summery hat that appears to feature a similar pattern to her mother’s dress.
In the caption, Mackintosh expressed that the past four weeks have been “the best” time.
“The first four weeks of your life have been the best four weeks of mine,” she wrote.
“Thank you for making me a Mummy darling girl.”
Taylor commented underneath the post with a blue heart emoji, while several others wished the couple congratulations on their new arrival.
“Congratulations to you all. What a sweet little poppet!” wrote fashion model Erin O’Connor.
Fellow Made in Chelsea star Binky Felstead commented with a line of heart emojis, while Oliver Proudlock remarked: “Yeah baby!!!”
Mackintosh was previously married to rapper Professor Green. The pair were married in 2013 before divorcing three years later.