The ceremony will take place at the Chapel Royal at St James’s Palace in London, where Louis’s older brother George was also baptised.
Their sister Charlotte was christened at the Church of St Mary Magdalene in Sandringham.
Louis, the Queen’s great-grandson, is fifth in line to the throne.
Now eight weeks old, he was born in London on 23 April, weighing 8lb 7oz.
The palace said: “The Duke and Duchess of Cambridge are pleased to announce that the christening of Prince Louis will take place on Monday 9th July at The Chapel Royal, St James’s Palace, London.
“Prince Louis will be christened by The Archbishop of Canterbury, the Most Reverend Justin Welby.”