The multi award-winning singer will be singing a two-song set in Israel this evening.
An official announcement was made in the week (May 16) ahead of the second semi final following claims earlier this week she had yet to sign a contract.
"We are pleased to finally confirm that the incomparable music icon Madonna will join us at this year's Eurovision Song Contest," said Eurovision's executive supervisor Jon Ola Sand.
"We know that it will be an evening to remember and can't wait to share it with everyone watching."
Madonna will perform her 1989 hit Like A Prayer, joined by a 35-strong choir, and new single Future from her upcoming album Madame X which features American rapper Quavo.
Eurovision host Assi Azar teased to Graham Norton on Radio 2: "I saw the rehearsal yesterday.
"It's an amazing show, what she's doing on the stage. She's literally taking over our entire stage, changing it completely."
He added: "I can say she's literally building a chapel inside our arena in 40 seconds. That's the time she has from the moment we get off the stage to the moment she goes on the stage. It's unbelievable."
Ahead of her performance, Madonna issued a statement in response to criticism of Israel hosting the event.
She said: "I'll never stop playing music to suit someone's political agenda, nor will I stop speaking out against violations of human rights wherever in the world they may be.
"My heart breaks every time I hear about the innocent lives that are lost in this region and the violence that is so often perpetuated to suit the political goals of people who benefit from this ancient conflict.
"I hope and pray that we will soon break free from this terrible cycle of destruction and create a new path towards peace."
Madonna is the latest interval act on Eurovision with past performers including Justin Timberlake and Aqua.
Michael Rice was chosen to represent the UK at Eurovision 2019 earlier this year.
He is no stranger to singing talent shows: Michael previously auditioned for The X Factor in 2014 and last year, he became the first winner of BBC One's singing show All Together Now.
During BBC's You Decide show, Michael and his song Bigger Than Us, written by Laurell Barker, Anna-Klara Folin, John Lundvik and Jonas Thander, were voted for by viewers to head to Tel Aviv in May.
The 64th Eurovision Song Contest will take place in Tel Aviv throughout May at the the Expo Tel Aviv.
The Semi Finals will be broadcast on Tuesday, 14 and Thursday, 16 May on BBC Four.
The Eurovision 2019 Final date is 18 May and will air live on BBC One.
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