The million-strong crowd came from around the world to participate in the celebration led by Pope Benedict XVI.
John Paul, who died in 2005 after 25 years as pope, was declared a "blessed" of the church during the special mass.
His beatification is the second last step in the process towards full canonisation and is the fastest in modern times after he was put on a 'fast-track' to sainthood.
An all-night prayer vigil in Rome's Circus Maximus ahead of this morning's mass featured testimony from the French nun at the centre of the miracle needed for John Paul's beatification.
Sister Marie Simon-Pierre says she was inexplicably cured from Parkinson's disease after a night of prayer to the pontiff not long after his death.
Full canonisation requires a second miracle and hundreds of faithful have reportedly come forward with claims.
The Mass was attended by 50 heads of government, including Zimbabwe's President Robert Mugabe.