In 1752, he succeeded Bishop Joseph Butler as Clerk of the Closet, and in 1757 the archiepiscopate of York, to which the office of Lord High Almoner was added, crowned his long series of ecclesiastical preferments.

A friendly witness, Bishop Thomas Newton, speaks of his being regarded as "somewhat haughty;" while Horace Walpole, describes him as "composed of that common mixture of ignorance, meanness, and arrogance."

John Newton, William Cowper's friend, when seeking to obtain ordination from him, found Gilbert "inflexible in supporting the rules and canons of the church."

His imperious character is illustrated by his refusal to allow the civic mace to be carried before the mayor of Salisbury in processions within the cathedral precincts, for which he claimed a separate jurisdiction, disobedience to which, it is said, caused an unseemly personal scuffle between him and the mace-bearer.

According to Newton, Gilbert was the first prelate to introduce at confirmations the practice of the bishop laying his hands on each candidate at the altar rails, and then retiring and solemnly pronouncing the prayer once for the whole number.