| Monica | Bellucci | Italian model & actress |
| Jonathan | Briggs | Will's best man, owner of whiskey business, 34, aka Johnno |
| Greg | Hastings | Wedding guest, school mate of Will & his friends |
| Julia | Keegan | The bride-to-be, 32, publisher of the online magazine The Downbeat, aka Jules |
| Miles | Locke | Wedding guest, school mate of Will & his friends |
| Curtis | Lowe | Wedding guest, school mate of Will & his friends |
| Conor | McGregor | Mixed Martial Arts & boxing champion |
| Peter | Ramsay | Usher, friend of Will from school, advertising exec |
| Will | Slater | The groom-to-be, famous TV actor |
| Jeremy | Swift | Wedding guest, school mate of Will & his friends |
| Alice | | Hannah's sister, deceased suicide victim |
| Angus | | Usher, friend of Will from school, developer |
| Aoife | | The wedding planner (pronounced Ee-fah), co-owner of the Folly |
| Araminta | | Jules' mother, Ronan's 1st wife, former actress, aka Mum |
| Bella | | Olivia's online alias |
| Ben | | Hannah & Charlie's son |
| Beth | | Younger cousin of Jules & Olivia, 15 |
| Callum | | Olivia's former boyfriend |
| Charlie | | Hannah's husband, good friend of Jules, geography teacher |
| Duncan | | Usher, friend of Will from school, venture capitalist |
| Ellie | | Girl Callum dated after breaking up with Olivia |
| Freddy | | Aoife's husband, chef, co-owner of the Folly |
| Georgina | | Duncan's wife |
| Hannah | | The Plus-One, Charlie's wife, mother of 2, former illustrator |
| Jess | | Friend of Olivia |
| Karen | | Florist friend of Hannah's mother, supplied flowers for Hannah & Charlie's wedding |
| Lottie | | Hannah & Charlie's daughter |
| Mattie | | Captain of the ferry to the island |
| Meg | | Jules & Olivia's aunt |
| Olivia | | Bridesmaid, Jules' younger half-sister, 19 |
| Oluwafemi | | Usher, friend of Will from school, surgeon, aka Femi |
| Piers | | Producer of Will's TV show |
| Ronan | | Jules' father, successful property developer, aka Dad |
| Rory | | Friend of Will, attended the pre-wedding stag party |
| Séverine | | Jules' father's fifth wife, French |
| Steven | | Man Olivia hooked up with |
