The trio join the previously-announced Anne-Marie and Olly Murs for the star-studded show - which will see no headliner and all acts offered equal billing - at London's Roundhouse on 18 November.
The event is being organised by mental health campaign #IAMWHOLE and is partnered by youth and mental health charities the Campaign Against Living Miserably (CALM), The Mix and YMCA, so 'Shape of You' hitmaker Ed is delighted to be opening the show with a special acoustic set.
He said: ''I'm so excited to be taking part in the first-ever Music 4 Mental Health event at the Roundhouse in November. Music is such an amazing way of taking the mental health conversation to a new level.''
And Ella is equally delighted to help such a great cause.
She said: ''I'm really excited to be performing at the Music 4 Mental Health event in November. Music is such a powerful way to bring people together - it's something we can all relate to and get involved with. I'm glad to be playing a part in raising awareness and support for the amazing charities working to end the stigma surrounding mental health.''
Former 'X Factor' champion James has spoken openly about his own mental health problems so the 'Say You Won't Let Go' hitmaker is ''proud'' to be a part of the gig.
He said: ''Mental Health and the issues that surround it can only be tackled by people speaking out about it. The Music 4 Mental Health fundraiser showcases the commitment being made to bring mental health awareness to people's attention and I'm proud to be a part of a cause that's very personal to me.''
The musical evening will be compered by Rizzle Kicks' Jordan Stephens, who is a founding ambassador of #IAMWHOLE.
Tickets to Music 4 Mental Health will be available from 8am from 8 September via Roundhouse.org.uk and Whole.org.uk. Tickets will cost £85 (subject to booking fees).
Twickets have been appointed the official resale partner for this event in a bid to curb touts.
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