The Archbishop of Westminster will bless more than 600 married couples to celebrate marriage as "an exclusive commitment and a life-long partnership between a man and a woman".
The couples - who have almost 20,000 years of marriage between them - are all celebrating their 10th, 25th, 40th, 50th or 60th+ wedding anniversaries this year.
During the 'Mass in Thanksgiving for the Sacrament of Marriage' this afternoon at Westminster Cathedral, they will renew their vows and pray for their families and all marriages before being blessed by Archbishop Vincent Nichols.
In his homily, Archbishop Nichols will say that marriage between man and woman is "sorely needed today" and serves society during the "hardship and deprivation today".
He will tell the couples marriage "fulfils husband and wife and is itself fulfilled in the life of the family".
"This witness you give, to the true nature of marriage in its natural and supernatural meaning, is a witness that is sorely needed today," he will say.
"It stands against those trends in our society which seek to undermine this understanding of marriage, reducing marriage primarily to a means of satisfying individual emotional needs.
"For a healthy society, those laws and conventions should always support marriage as an institution characterised by an openness to children and the responsibility of fathers and mothers remaining together to care for children born into their family.
"Strong families serve society by bringing forth healthy children and maturing young adults, by being a rich source of a compassion for sick members, of support for others in time of crisis and of care for the elderly and the dying. Stable families are the first and best answer to many of the personal and social consequences of hardship and deprivation today.
"Families are often best placed to respond to those needs. No intelligent government can continue to ignore the urgent priority of giving support and practical encouragement to marriage and family stability as the first response to growing social needs."