The company said that a bid of CAD$38.1bn had trumped a hostile bid by another rival in the aluminum sector, Alcoa, earlier in the week.
Alcoa is believed to have offered around $28.8bn, a sum that Alcan executives and many industry experts said significantly undervalued the company.
Rio said that the deal was likely to help it diversify beyond its strengths mining minerals such iron ore and copper, but likewise, many beleive that the prospect of taking on the business's packaging operations is unlikely to be of interest.
The deal means that Rio Tinto will make an initial offer to acquire Alcan's outstanding shares at a cash price of $101 per share, a value that Alcan's board of directors is said to have agreed on.
This figure represents a premium on the existing trading price of the shares, which are currently trading at just at $98 per share, well up on the $37.42 low for the year.
In 2006, Alcan Packaging registered sales of $6bn - out of a total of $23.6bn for Alcan as a whole.
Of this figure beauty packaging represented 13 per cent of the division's revenues.
The acquisition leads industry experts to believe that the company's packaging division, which is largely concerned with beverage can production, and to a lesser degree cosmetics packaging, will eventually be spun off.
Currently the mining industry is benefiting from soaring metal commodity prices, putting many of the larger and healthier metal companies in a position to buy up smaller or struggling players.