A devout Australian couple married for 55 years have explained the joys of sex to Pope Francis and senior members of the Catholic Church while calling for the inclusion of homosexual couples within the faith.

Ron and Mavis Pirola, former members of the Pontifical Council for the Family and directors of the Australian Catholic Marriage and Family Council, were one of six couples chosen to address 200 bishops from around the world at the Vatican's Synod on the Family on Tuesday.

Mavis and Ron Pirola have called for the Catholic Church to welcome homosexual couples and for married couples to recognise the importance of sex.

The Sydney couple, who have four children, said married couples need to view sex as an essential foundation for their relationship and spirituality as sexual attraction brought them together and has sustained their marriage for more than half a century.

"That attraction that we first felt and the continued bonding force between us was basically sexual. The little things we did for each other, the telephone calls and love notes, the way we planned our day around each other and the things we shared were outward expressions of our longing to be intimate with each other," they told the crowd, which included Archbishop of Melbourne Denis Hart, the only Australian prelate in attendance.