Trustees announced a new partnership deal with Cadw, the Welsh government's historic environment service, resolved "short-term problems that gave rise to concerns over the future" of the museum at Caernarfon.
Last week, trustees said they had not received funding since February.
Culture and Sport Minister John Griffiths said he endorsed the deal.
A statement on the RWF Museum website said the partnership with Cadw will "see the Royal Welch Fusiliers Museum funded to provide visitors to Caernarfon Castle with access to the Welsh government accredited museum and to provide an education service for schools".
The museum, which has been based at Caernarfon Castle since the early 1960s, charts the 300-year history of the RWF, dating back to William III.
The regiment was one of the three Welsh infantry regiments to be merged in 2006 to form The Royal Welsh, though the name lives on as the infantry are known as 1st Battalion The Royal Welsh (The Royal Welch Fusiliers).

Bayley, 29, defeated Ukraine's world number one Maksym Nikolenko 3-2 in the class 7 final.
Wilson, 21, overcame former world champion Richard Csejtey, from Slovakia, 3-2 in the class 8 final.
Another Briton, Martin Perry, lost to France's Bastien Grundeler in the class 6 semi-final, but took bronze.
Find out how to get into disability sport with our special guide.
The Royal Welch Fusiliers Museum (RWF) has been saved from closure after its funding was secured.
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British Paralympic table tennis champion Will Bayley and Rio 2016 team-mate Ross Wilson both won singles gold at the PTT Bayreuth Open in Germany.