[1] In 1420, Guy XIV, only just fourteen years old, was the second person to put his signature to the petition sent to the king of England to demand the release of Arthur III, Duke of Brittany, the future constable, who had been a prisoner since the Battle of Agincourt.

On 8 June 1429, at Selles-en-Berry (Selles-sur-Cher), he rejoined the royal army which reunited Joan of Arc and the duke of Alençon to seek the liberation of the Loire Valley after the raising of the siege of Orléans.

With his brother André de Lohéac he followed the sovereign to Reims and assisted at the coronation of Charles VII of France on 17 July 1429, replacing Philip the Good, count of Flanders (who was also the Duke of Burgundy).

Guy XIV assisted at Tours, on 14 January 1446, in a notable combat before Charles VII, between the Englishman Jean Chalons and Louis du Bueil, with the latter being killed.

As his ancestors had founded the four canonical-prebendaries of Saint-Jean-de-Langeais, it was up to him to provide the residency privileges which they dispensed, as a result of which divine service was no longer assured.

The mandate of dispensation for the marriage of Guy XIV and Françoise of Dinan said to be of Thouars from her mother's name, and for their absolution from certain bans, is dated 17 December 1450 and addressed to the bishop of Vannes.

In order to assert better his precedence on the viscountcy of Rohan to the States of Brittany, Guy XIV de Laval, seigneur of Brocéliande, pretended, via his parent, to be descended from the ancient kings of Armorica Conan and Ponthus.