The village of Kinloch passed into the hands of a community trust 14 months after the 17 eligible voters among the island's 29-strong population had voted 15-2 for greater autonomy.
Rum has been owned by conservation agency Scottish Natural Heritage and its predecessor, the Nature Conservancy Council, since 1957 and run as a national nature reserve.
Fliss Fraser, a spokeswoman for the trust, said: "This is a day the community of Rum has been hoping for and working towards for more than ten years. We are now building a new relationship with SNH, as a neighbour on the island, rather than our landlord."
Andrew Thin, the chairman of SNH, said: "SNH now looks forward to working in partnership with the islanders to help them develop a strong and successful community."
The transfer of ownership is expected to pave the way for crofting to resume on Rum.