As a vicar, the priest appointed by the bishop acts in the name of the diocesan bishop, and as vicar general, that priest possesses the same executive authority as the diocesan bishop across the whole of the diocese as belongs by church law to the diocesan bishop.
A vicar general can perform all the same administrative acts as the bishop, unless the bishop has reserved any specific acts to himself, or which may require the special mandate of the bishop to be undertaken.
A priest appointed as vicar general can exercise a significant range of executive authority in a diocese, but it is not absolute. When exercising any authority or carrying any act, a vicar general does so always in the name of the diocesan bishop (hence the use of the title vicar) and according to the ‘mind and will’ of the diocesan bishop. A vicar general never acts according to his own determinations; he must always act as the diocesan bishop would act.
How this works in practice will vary from diocese to diocese, according to the needs of each diocese. Some dioceses have a full-time vicar general; other dioceses have vicars general who also have other roles, such as continuing to be a parish priest. The role of vicar general requires a close working relationship between the diocesan bishop and the priest appointed as vicar general to ensure that the bishop’s vicar general understands the thinking of the bishop on those things that impact on the life of the diocese.
In the Diocese of Maitland-Newcastle, parishioners will encounter the vicar general most often when he presides over the celebration of the confirmation on behalf of the bishop, though there may be other public occasions when the vicar general attends an event on behalf of the bishop.