The 73-year-old worked with Benny Andersson on the music for the movie, which utilises the iconic quartet’s extensive discography.
With many of ABBA’s most famous tunes used up in the 2008 first movie, this time around we have more lesser-known songs – among them My Love, My Life; which is sung by Lily James, Amanda Seyfried and Streep towards the end of the film.
It’s left audience members in floods of tears, with the movie’s mother-and-daughter theme more raw than ever.
“Meryl is of course a wonderful singer and she sings My Love, My Life so beautifully,” Ulvaeus said.
“But she is… Is there a better storyteller than she? I don’t think there is.
“She gives those words meaning that I never could have hoped for.”
Some of the lyrics to the songs, such as on My Love My Life and I’ve Been Waiting For You, were tweaked to fit the context of the story; which Ulvaeus said was “great fun” to work on.
“We are using songs that are not that well known from the ABBA catalogue so for instance in a song called I’ve Been Waiting For You, I tweaked, I rewrote the verses a little,” he explained.
“It was great fun writing for a particular scene in the movie and I think it’s come out so well.”
The music may not be as famous this time around, but that hasn’t stopped it from selling: the official soundtrack album for Mamma Mia: Here We Go Again is heading for the Number 1 spot on the UK album chart this Friday.
The good news comes after the movie hit No1 on the box office listings over the weekend, generating around £13 million in the UK alone.
Streep, James and Seyfried are joined in the cast by returning fixtures Christine Baranski, Julie Walters, Stellan Skarsgard, Colin Firth, Pierce Brosnan and Dominic Cooper; with Cher and Andy Garcia joining for the first time.
The sequel has also had much more positive reviews than its predecessor, after many – including Seyfried – were skeptical about its prospects.
Mamma Mia: Here We Go Again is out now.