Ms Middleton, 33, is marrying James Matthews, 41, an investment manager, in a church on a private estate in Berkshire owned by Richard Benyon, the Conservative who was the richest MP in the last parliament.
It's been described as the society event of the year - and brand experts believe the build up to the wedding of Pippa Middleton and James Matthews has already been a huge boost to the couple's public profile.
William and Kate's son Prince George will act as page boy while their daughter Princess Charlotte will be one of the bridesmaids.
Only the weather was beyond the bride's control, and if she had been anxious about a downpour spoiling her big day, she would have felt relieved when, by 4pm, the sun emerged from behind the clouds, auguring a bright, sunny morning when she makes that six-mile journey to the church as Miss Pippa Middleton and returns as Mrs James Matthews.
As Pippa's semi-royal wedding is not actually royal, her ceremony won't be broadcast live on TV like her sister's.
The Duchess of Cambridge has already admitted she is a little anxious about how her children will behave.
Pippa Middleton and her fiance James Matthews. The royal youngster has only just turned two and Kate has described her as having something of a feisty side.
Does the Queen have a role? Prince Charles and his wife Camilla also plan to miss the event, which is drawing only the younger royals.
The guest list will include the second and third-in-line to the British throne along with a host of VIPs and celebrities, so the Middleton and Matthews families are taking no chances when it comes to safety and security. In November he released an unusual letter calling for the press to stop intruding into her private life and saying he would do everything possible to protect her from unwanted scrutiny.
They had dated for less than a year - although the couple had briefly been an item in 2012 as well - when he got down on one knee and asked her to marry him.
And let's not forget why - Pippas butt stole the show at Will and Kate's wedding. Some expect Harry to attend the church ceremony solo, than bring Markle to the reception that follows.
Despite her nerves, Kate said she was looking forward to the wedding of her sister.
A number of British-based designers are thought to be likely contenders for one of the most highly anticipated commissions of the year, including Jenny Packham, Erdem, Giles Deacon and Philippa Lepley.
Hatmaker to the stars Stephen Jones - also known for his veils - may also be involved.