Coadjutor bishop
In 1895 Lenihan was appointed Coadjutor bishop to Bishop Luck, on whose death (early in 1896) he succeeded as ordinary and was consecrated a bishop on 15 November 1896 at the relatively young age of 38. In 1899 Lenihan visited Rome and Ireland and secured more priests for the diocese. He opened Sacred Heart College, Auckland in 1903 and in 1905 undertook the completion of St Patrick's Cathedral, Auckland. This was accomplished in 1907, the complete building being dedicated in 1908 by Cardinal Moran, Archbishop of Sydney. Lenihan again visited Europe and North America in 1908 when he attended the celebration of the golden jubilee of Pope Pius X and the Eucharistic Congress in London.