The 23-year-old singer will take on the important role when the raven-haired beauty ties the knot with Snow Patrol star Johnny McDaid later this year after the 'Lego House' hitmaker introduced the pair to each other, and Ed is also thought to be in line for the best man job.
A close friend of the former 'Friends' star said: "Not only is Ed great mates with Johnny, he is a close friend of Courteney's.
"Ed said yes immediately when asked. Johnny's other best pal, singer Foy Vance, is also an usher.
"It's between him and Ed for best man -- they'll probably share it."
Courteney, 50, was previously married to David Arquette from 1999 to 2013 but she is said to be happier than ever since meeting 38-year-old musician Johnny.
The pal added to The Sun newspaper: "She has never been happier.
"And even though it's her second marriage, she would like people important to her to be there."
Johnny proposed to Courteney - who has 10-year-old daughter Coco with ex-husband David - in June after just six months of dating.
The 'Don't' hitmaker previously let slip that the couple had moved in together and he is said to have been living in the actress' Malibu home rent-free recently.
It was recently revealed that Courteney is keen to get married in Ireland after falling in love with Ashford Castle in Lough Corrib, Galway, when visiting Johnny's family recently.