During the outbreak of the Second World War, Archbishop Masson made a vow that if Ceylon were to be protected from major conflict, he would build a Votive Basilica under the title Our Lady of Lanka.

The archbishop was delighted and in 1946 he obtained approval from the then Pope, Pius XII, for the construction of a basilica in honour of Our Lady of Lanka.

Masson died the following year and his successor Archbishop Thomas Cooray took on the responsibility of ensuring his predecessor's vision was realized; In 1948 Pope Pius XII established the Mary Immaculate, to be known as Our Lady of Lanka, as the principal Roman Catholic patroness of the island.

The front porch has six pillars representing the dioceses during WWII which were Colombo, Galle, Jaffna, Kandy, Chilaw and Trincomalee;[7] and a cross with a bronze Christ figure by Sri Lankan artist Leila Peiris, set against a circular glass in a spider web design, within a stupa-inspired frame.

The cruciform structure features a central dome with a cross of the Eastern Oriental Church, granite walls, and wooden doorways with Indian architraves.

Inside, a life-sized statue of Our Lady of Lanka carved by Thedim holds the infant Jesus with a golden rosary.

These include the four convents, the Museum and Jubilee Hall, the Retreat House, the new and old grottos of Our Lady of Lourdes, the bathing pond and lake, the old church etc.