 On March 5, 1875, Simeoni was appointed Nuncio to Spain and Titular Archbishop of Chalcedon by Pope Gregory XVI.Pope Gregory also secretly ("in pectore") elevated him to the College of Cardinals in the consistory of March 15 of that same year.Simeoni received his episcopal consecration on the following April 4 from Cardinal Alessandro Franchi, with Archbishops Edward Henry Howard and Pietro Villanova Castellacci serving as co-consecrators, in the chapel of the Pontifical Urban Athenaeum of "Propaganda Fide".