The National Galleries of Scotland (NGS) said donations had come from as far afield as Los Angeles and Hong Kong to raise £4m to secure the painting.
Public donations totalled more than £260,000, with the biggest donor the Heritage Lottery Fund, who gave £2.65m.
The work, which was being sold by drinks giant Diageo, will be hung in the Scottish National Gallery in Edinburgh before going on tour.
The fundraising bid was launched in February after Diageo announced their intention to sell it.
The 163.8cm x 169cm painting, which features a Highlands red deer stag with 12 points on its antlers, has been in private or corporate hands since it was painted in 1851.
NGS said it was overwhelmed by the public response to the campaign, with donations made from across the world, including from Anchorage and Queensland.
Private trusts and foundations also gave £634,000, while the Art Fund donated £350,000 and the Scottish government £100,000.
Sir John Leighton, director-general of the National Galleries of Scotland said: "We are thrilled that we have been able to secure this iconic work for the national collection.
"The enormous support from the public has been incredible with donations coming from all over the world and from the length and breadth of Scotland and the rest of the UK.
"Thank you so much to everyone who has donated. Your gift has helped to ensure that this magnificent work will be enjoyed by millions of people for generations to come."
The National Lottery and Scottish government have also given £175,000 to enable the painting to go on tour across Scotland. NGS said plans were being for the tour to a "number of venues across Scotland", starting later this year.
Diageo first said it was selling the painting in November, leading to speculation it could fetch in excess of £10m on the global art market.
The drinks firm later agreed to reduce its selling price from £8m to £4m to help it remain in public view in Scotland.
The Monarch of the Glen, which features a "royal stag", is thought to be set in Glen Affric.
The NGS describe the work as "an important Victorian picture that has taken on various layers of meaning, which include its use in advertising and as a Romantic emblem of the Highlands of Scotland."

He claimed First Minister Carwyn Jones was saying "I told you so" while Plaid Cymru was using the poll's outcome as an "excuse" to call for independence.
Labour and Plaid had a "little Britain mentality" when a "globally facing Britain" was needed, Mr Davies wrote.
He made the comments in an article for The Times newspaper's website.
On Thursday, Welsh Government economic advisor Kevin Gardiner said some people were "perhaps unduly pessimistic" after the vote to leave the EU.
Within hours of the Brexit result being announced on June 24, Mr Jones said he feared it would cost Wales jobs.
In his article, to be published on Friday, Mr Davies said the first minister had been "particularly vociferous in his doom-laden economic forecasting, and in denigrating those who chose to leave".
"He has closed the doors on cross-party negotiation and now, having lost his nerve, seems unable to negotiate a deal for Wales, resorting instead to finger-wagging and pronouncements of 'I told you so'," Mr Davies wrote.
Plaid Cymru's call for independence "betrays how out of kilter they are with the needs of Welsh communities", he added.
"The prophets of doom and the independence mongers alike are wrong to take such a warped view of referendum result."
Mr Davies urged his political opponents to "lift their eyes to the sky and consider the limitless potential that now lies ahead of us and to embrace the outcome".
He added: "Instead they seem intent on clinging to a little Britain mentality. A globally facing Britain is what is now needed."
Sir Edwin Landseer's iconic Monarch of the Glen has been saved for the nation.
[NEXT_CONCEPT]
"Prophets of doom" and "independence mongers" are taking a "warped view" of the Brexit vote, Welsh Conservative leader Andrew RT Davies has said.