The Society of St Pius X - a rebel group of ultra-conservative Catholics - was excommunicated after four bishops were ordained without Pope Leo's approval on Wednesday.
The group has been unrepentant over the schism with Rome, saying Leo had failed to hear its concerns.
"There will one day be another Pope who opens the door and welcomes us back. Just like Pope Benedict," Georg Kopf said at a mass held in the northeast Swiss town of Wil.
Established in 1970, the group - which is based in Switzerland but has followers worldwide - accuses the church of straying from the true faith.
It practices old-style Latin mass and does not believe in formal dialogue with non-Catholics.
The group has endured a rupture with the Vatican before.
In the late 1980s, its founder Marcel Lefebvre consecrated four bishops without the approval of Pope John Paul II, leading those involved to be excommunicated.
They were welcomed back in 2009, however, when Pope Benedict XVI sought unification by lifting the judgement.
"I am convinced that there will be another Pope like him who will give tradition its rightful place again. Of course, we'd like that to happen tomorrow," Kopf said.
The Vatican said dialogue was offered to the group ahead of the schism and the step of ordaining bishops without church approval was considered so grave excommunication was automatic.
"Nothing that happened on July 1 was intended to establish a parallel church or to break with Rome," Kopf said in his sermon given in German.
"On the contrary, it was precisely out of love for the church and the Pope that these ordinations were carried out, in order to look after the salvation of souls."
4°C