The Stewarts continued to finance his studies in London, where Cregan was a pupil of Martin Archer Shee.

William Stewart Cregan, the couple's fourth son, exhibited twice with the Royal Hibernian Academy (RHA) in 1860 and 1872.

When he retired, Cregan moved to 109 St Stephen's Green, and then later to a smaller house at 22 Lennox Street.

The Dublin National Gallery has a copy by him of Sir Joshua Reynolds's portrait of Master Crewe.

[2] Towards the end of his tenure, Cregan was criticised for the unsuccessful exhibitions and the growing debts of the RHA as well as his efforts to reform the organisation.

Cregan supported the academy's secretary and leading reformer, Michael Angelo Hayes who was not popular with the older members.

Later in his life, he faced competition from Stephen Catterson Smith, but Cregan continued to paint and was completing a commission for an altarpiece when he died.