Martin Ssempa (born 3 January 1968) is a Ugandan charismatic pastor, activist, and the founder of the Makerere Community Church. Ssempa first came to international prominence in 2010, after a presentation video he made at his church, which showcased his opposition to homosexuality, went viral.

Martin Ssempa was born in Nalusali village in Masaka District in 1968, the youngest of eight children to a Muganda mother. He did not know his father, who was Indian and expelled from the country during the presidency of Idi Amin. Ssempa was named after his grandfather. His mother, a teacher, raised her son alone and he changed schools often as a child. Ssempa went to Kimanya Primary School in Masaka and St. Peter's Primary School in Nsambya. He then went to Rubaga Boys' Secondary School, before he completed his A level at Namilyango College.

In 1988, Ssempa was admitted to Makerere University, from where he graduated in 1991 with a bachelor's degree in social science, specialising in sociology. In 1992, he started studying at Philadelphia Biblical University (Cairn University since 2012), obtaining a Master of Arts degree in biblical counselling. Around 2008, Ssempa received an honorary PhD from Cairn.

In 1997, Ssempa was part of a student group at Makerere University that founded a weekly musical gospel rally, SANJA (short for Saturday Night Jams), following concerns over increased alcohol consumption and sex activity during nightclub visits by students. In 1999, Ssempa and four other students renamed SANJA to Prime Time, gradually becoming an general entertainment event, ranging from music, comedy, and poetry acts, as well as speeches by local businesspeople, pastors and politicians, as well as a HIV awareness program, featuring testimony from pastors, doctors and those living with HIV.

While in the United States, Ssempa met his wife Tracey, a missionary at the time, whom he married on 25 April 1992. According to a voter registration application submitted on 6 July 2012, Ssempa is a United States citizen.

In December 2018, Ssempa announced that he will be "transitioning" to the alternative name Gabriel Baaba Gwanga'Mujje eri Yesu starting 2019. According to Ssempa, the first name was chosen to mean "I stand in God's presence" (a quote by the archangel Gabriel), the middle name as in "Father of a new generation", while the last name is Luganda for "Nations are summoned to Jesus". In a 2019 interview on the Urban Television program Urban Today, Ssempa stated that the name change was motivated by "curiosity" and to more openly show his Baganda background. He remained known by his original name, but occasionally used the alias during interviews and speeches.

Ssempa's religious interests began when he joined a bible study group in school, in hopes of starting a relationship with a female schoolmate, later recalling "[M]y focus was not on Jesus but on the girl herself". While he failed to enter a relationship with the schoolmate, Ssempa credits the bible study with making him a born-again Christian. He initially sought to become a Catholic priest, but at age 18, he instead joined a Baptist congregation.

During his time at Makere University, both Ssempa's brother and sister contracted HIV. Ssempa sat by their beds as they grew sicker. When they died in 1990, he blamed their promiscuity and feared that his lifestyle would also lead to his death via AIDS. Ssempa gave up on his initial plans of becoming an international performing artist and converted to Evangelical Christianity at the Wandegeya Baptist Youth Center. He travelled the country with a drama group that performed in schools in an effort to educate students about AIDS.