Webber will be assisted by the pair and casting expert David Grindrod during callbacks for the show, which is searching for a fresh face to play Jesus in the upcoming arena tour of rock opera Jesus Christ Superstar.
Forty acts will progress to the next stage, a week-long 'pop up' performance school that's said to 'bring out the very best in acting and vocal ability'.
Webber will then choose a number of finalists to compete for public votes in a series of live shows, which will have a seperate judging panel.
The theatre impresario, who will oversee the entire casting process, said: "I’m pleased to appoint David, Jason and Melanie to assist me with the candidates during Callbacks as I select my final 40 to go further for intensive training.
"They will be using their unique arena and stage experience to help me narrow down my choices for the live shows."
Former Spice Girl Mel, who earned an Olivier Award nomination for her role as Mrs Johnstone in Blood Brothers, commented: "I'm a huge fan of Andrew's incredible work over the years.
"I am honoured and excited to work along side him helping to find a performer with the raw talent and charisma to play the title role of Jesus."
Jason - who has starred in several West End shows including Joseph and the Technicolor Dreamcoat, Chitty Chitty Bang Bang and Priscilla, Queen Of The Desert - added: "We’ve got an amazing challenge ahead of us, helping Andrew in his quest to find someone to play the title role of Jesus in the new arena tour of Jesus Christ Superstar.
"I can’t wait to start working with Andrew again."
Superstar will air on ITV1 this summer.