The announcement comes few weeks after Mutharika ,77, won the 2014 disputed presidential election with 36 percent.
President Mutharika is planning a private traditional wedding ceremony on Saturday to be blessed at St Michaels and All Angels CCAP Church in Blantyre and reception at the Mutharika family home at Ndata farm in Thyolo district, State House indicated in a statement on Friday.
But critics have doubted the privacy of the wedding arguing his brother, late president Bingu wa Mutharika, also made similar claims when marrying former Tourism Minister Callista Chapola-Chimombo in 2010, but the ceremony ended up in a lavish way at the State House.
President Mutharika and Maseko have on several occasions shown their affection publicly.
President Mutharika, who has three children, has stayed a widower for about thirty years raising speculations that he was gay.
But Mutharika had repeatedly trashed the claims.
Maseko on the other is said to have one child, but details or her previous marital status remain sketchy.
President Mutharika hails from Kamoto Village, Traditional Authority Chimaliro in Thyolo district while Maseko comes from Kapasule Village, Traditional Authority Msamala in Balaka district.