Thomas Donald Mackay Shaw, 3rd Lord Craigmyle, has died aged 74. He played a leading role in galvanising Catholic laity into effective action in charity and politics, while quietly giving away his fortune. In 1993, the Pope recognised the extraordinary breadth of his work and generosity by making Craigmyle a Commander of

the Order of Pius IX - the highest Pontifical honour for any living layman.

One of Donald Shaw's grandfathers had been Lord Advocate, as Lord Shaw of Dunfermline. The other was the first Earl of Inchcape. However, Donald was shaped more by his shyness, and always found comfort in religious devotion.

Leaving Eton during the war, Donald entered the Royal Navy Volunteer Reserve. He trained to fly for the Fleet Air Arm, but couldn't manage the examination in 1944 - something he put down to the concurrent death of his father, 3000 miles away.

Craigmyle took up his seat in the House of Lords wearing the bell-bottomed uniform of a sublieutenant, while living only on his rating's pay. ''The Blue Jacket Peer'' was then pushed through Trinity College Oxford in post-war haste, and went to India to work for the family firm, McKinnon Mackenzie.

One day in Calcutta Cathedral, he found himself the alter server to Fr Robert Llewelyn, and learned that Llewelyn needed 200,000 rupees for a school chaplaincy. Craigmyle had received a cheque for #15,500 the day before, almost exactly the same amount, so he gave it to Fr Llewelyn. This sort of fatalistic approach to need and charity was typical. In later life he would ask: ''And who arranges the coincidences?''

While in India he met Anthea Rich, a recent convert to Catholicism, whom he married in 1955. The next year he followed her father, Cannon Edward Rich, to Rome.

Settling in London, Craigmyle opened a dizzying array of charitable and commercial enterprises from Scotland to Namibia. There were few causes which did not benefit from Craigmyle's influence, either in the boardroom, the House of Lords, or through sheer munificence.

At night, Craigmyle donned his St John's Ambulance uniform to go on duty as a first-aider. He recommended this as a way to see opera.

As a yachtsman, Craigmyle backed the ''Red Duster'' syndicate, trying to bring the America's Cup to Britain. Embarrassingly, he thrashed the contender soundly in his own yacht, Norsaga.

All this time, Craigmyle was drinking heavily. By 1970 alcoholism had overcome him. Recognising the situation, he spent six years drying out - which meant dealing with his terrible shyness. Emerging slowly from that awesome cocoon, he began again, child-like, picking up the threads where he had left off, gradually starting up new ventures.

Aged 52, he redoubled his efforts with the bagpipes, and taught himself the piano. He wrote music and set reels which have entered the dance repertoire. And he threw himself into the work of the Order of Malta, becoming President of the British Association in 1989.

But most of all, Craigmyle sought to help the dying and the destitute, especially alcoholics.

In a ''dry house'' for alcoholics which he himself had endowed, Craigmyle had given away his own clothes. A visiting bishop mistook the residents for town councillors. Meanwhile, on the night-time soup-run, Craigmyle's identity was never revealed. ''How long have you been homeless, Jock?'' he was asked.

With roots in Rothiemurchus, the pull of the Highlands proved irresistible. In 1964 Craigmyle sold his family estate near Selkirk to rebuild a ruin by Loch Nevis. He was happiest there, composing and piping, lifting lobster-pots, and baking bread and bannocks.

He is survived by his wife and six of his children.