According to local news report, Mr Kamanya shot himself around 3:30 this morning at his house in Area 10, Lilongwe after losing the Lilongwe Msodzi North Parliamentary elections this week.
"We had to break the door to his kitchen where he had locked himself up," Kamanya's friend also a member of Banda's People's Party – told Zodiak broadcasting.
In the suicide note, the former minister reportedly said he took his life because of misunderstandings related to politics and outlined how his wealth should be distributed to beneficiaries.
However, his spokesman denied reports that his suicide was linked to him apparently losing his parliamentary seat.
Confirming the incident, Lilongwe Police Officer-in-Charge Richard Luhanga said, "we received a report at around 4 a.m. (local time) this morning that Hon. Kamanya had shot himself, as for the reasons he has left a suicide note."
He, however, did not disclose the contents of the suicide note, saying: "Family members can disclose that."
Meanwhile, the country's president, Joyce Banda has said that the elections have been marred by "serious irregularities", including vote-rigging and computer-hacking, while also calling for an immediate manual audit of the results.