The Duchess gave birth on 23 April in London and has been keeping a relatively low-profile since.
Prince Louis will be christened by the Archbishop of Canterbury, Justin Welby, on Monday 9 July, Kensington Palace has announced.
James Brookes, a royal expert, told British tabloid The Daily Express that pictures of Prince Louis' christening were likely as the Duke and Duchess of Cambridge sought to compromise between their desire for privacy and public desire for information about the event. James, Viscount Severn, was the first baby to wear the new outfit at his christening in 2008. Both George and Charlotte were both also baptised by the Archbishop of Canterbury. It's the same spot that Prince George had his big day - although Princess Charlotte's was at the Church of St Mary Magdalene in Sandringham.
If his siblings' ceremonies are anything to go by, Prince Louis' christening will be a private affair.
George held William's hand, while baby Charlotte was pushed by Kate in a vintage pram, previously used for two of the Queen's children.
At a christening already heavy with memories of Diana, Princess of Wales, the choice of Laura Fellowes confirmed predictions that the Duke would want a member of his mother's family to be a godparents.
The tradition of wearing the gown started in 1841 when the original gown was made for Queen Victoria's first child Princess Victoria's baptism.
While the Duke and Duchess of Sussex were present in the celebration, Prince William and Kate Middleton didn't attend the event.