She played a memorable supporting role at sister Kate’s 2011 wedding, but Pippa Middleton will take centre stage on Saturday at what looks to be the high society event of the year.

The 33-year-old is marrying a wealthy financier at the oh-so-English 12th-century church of St. Mark’s in the village of Englefield, west of London — with a guest list of young A-list royals and reality TV stars looking on.

The Middleton sisters Pippa and Kate at Wimbledon. Picture: AP

Prince William, a future king, will be there with his wife Kate, now formally known as the Duchess of Cambridge, and their two children, Prince George, 3, as pageboy and two-year-old Princess Charlotte, as bridesmaid.

There is widespread speculation that Prince Harry will bring his girlfriend, American actress Meghan Markle, to showcase their budding romance.

Middleton is marrying hedge fund manager James Matthews, who proposed last summer during a trip to England’s scenic Lake District, in what is expected to be a $500,000 gathering.

Pippa Middleton and James Matthews will wed on Saturday (AEST). Picture: PA

They had dated for less than a year — although had briefly been an item in 2012 as well — when he got down on one knee and asked her to marry him.

The wealthy Matthews has shunned the spotlight, but his brother Spencer Matthews has compensated for that with his role on the reality TV show Made in Chelsea. He is expected to be the best man.

Pippa Middleton will be wed in St Mark's Church in Englefield, Berkshire. Picture: PA

All eyes will be on exactly what style of dress Middleton will wear, with a number of British-based designers 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.

Middleton is expected to wear a traditional, embroidered gown, most likely with the spectacular beadwork and detailing that mark high-end British fashion.

Pippa is expected to change into something jazzier for the reception planned at her parents’ country estate in Bucklebury, 80km west of London.

Pippa Middleton shot to fame after carrying her sister the Duchess of Cambridge's train. Picture: PA