The couple ' who have been dating since September 2009 ' have sent out invitations to their friends and family for the ceremony, which will take place in India later this month.
The white embossed cards said: "Meet you in Delhi in October. Dates to follow. Please allow seven days for this event."
The pair - who got engaged at the Taj Rambagh Palace hotel in Jaipur on New Year's Eve last year (31.12.09) and were blessed in a spiritual ceremony in the country days later - are reportedly planning a Hollywood-meets-Bollywood theme and have enlisted celebrity wedding planner Mindy Weiss to arrange their big day.
A source told the Daily Mirror newspaper: 'Expect the most vibrant wedding of the year. It will be a mix of traditional Hollywood glamour with Katy's hair and dress, plus Indian touches like henna art on her hands and feet, an Indian tiara and hair brooches.
'About 75 to 100 guests will be staying at a resort in India and the ceremony is going to be held at an ashram.'
And guests at the glitzy bash will include comedian David Walliams, singers Morrissey and Rihanna, rocker Noel Gallagher and presenter Jonathan Ross.