Pienaar will be among a host of speakers listed on the programme including Amore van der Westhuizen and SA minister of Sport and Recreation Fikile Mbalula.
The national anthem was sung before an SA Police Service representative draped the casket in the SA flag.
President of the South African Rugby Legends Association Gavin Varejes said Joost van der Westhuizen was a fighter to the very end.
Varejes was the first speaker to pay tribute to Van der Westhuizen.
“I don’t want to mourn his death, but celebrate his life. I remember that day in 2011 when Joost came to share the terrible news of his illness with me,” said Varejes.
“The words give up were never in his vocabulary.”
Earlier, a private service for close family and friends ended shortly after 11am, and the casket of Van der Westhuizen was escorted to Loftus.
Van der Westhuizen passed away on Monday after a long and courageous struggle with amyotrophic lateral sclerosis (ALS), a form of motor neurone disease (MND), for the past six years. He was 45 and leaves behind two children, Jordan (13) and Kylie (10), as well as his father Gustav, mother Mariana, and brothers Pieter and Gustav.