The pontiff will say an ecumenical prayer, which reflects the Holy Father's bid to unite Christinians of different denominations.
Vatican figures show that 25 percent of the Latvian population are Lutheran, 21 percent are Catholic and 11 percent are Orthodox.
Pope Francis will also meet with Latvian President Raimonds Vejonis and will give a speech to representatives of the government and the public.
Later on, the pope will visit the Freedom Monument in Riga and travel to Aglona to celebrate the Holy Mass, with around 32,000 people registered to attend the event, although the local Church expects twice as many people to come.
The Holy Father's visit might be overshadowed by the sexual abuse scandal, with Latvian officials saying in early September they had arrested a priest suspected of rape.