Family, friends and fashion industry luminaries turned out to remember the designer, who committed suicide in March.
Sir Mick, 70, also spoke words of tribute at the service, held at St Bartholomew’s Church in Manhattan, New York, on Friday evening.
L'Wren's brother Randy Bambrough, actresses Ellen Barkin and Sarah Jessica Parker and fashion personality Andre Leon Talley were among others to share their memories.
Poems were read by L'Wren's niece, Hannah Bambrough, and Sir Mick’s son, James Jagger.
The Rolling Stones singer's grandchildren, Mazie and Zak, read Psalm 23.
His backup singer Lisa Fischer sang Amazing Grace.
The rock icon's bandmate Ronnie Wood, 66, was also at the service, which was followed by a reception.
Others attending included actresses Julianne Moore, Meg Ryan, Olivia Munn and Renee Zellweger, Vogue editor Anna Wintour, film directors Martin Scorsese and Baz Luhrmann and Vanity Fair editor Graydon Carter.
Fans lined against barricades to take photos.
A small private funeral was held for L'Wren in LA two months ago.
