Anyone who buys a ticket will get a seat of the same value entirely free of charge for the summer international at the home of Welsh rugby.
The deal is being offered by the Welsh Rugby Union for the send-off international which is the last game played in Wales by the World Cup squad before they fly off to New Zealand for rugby's greatest competition.
The game will offer fans the chance to send Wales on their way with a resounding cheer before they take on South Africa in their opening RWC Pool match in Wellington on September 11.
Argentina will also be using the game as a final encounter to test the mettle of their stars before they start their own journey to New Zealand.
The Pumas are renowned for causing World Cup upsets and made it through to the semi-finals in 2007, where they lost to South Africa, but went on to claim third place by beating host nation France 34-10 in the bronze final at Parc des Princes.
The buy one get one free offer will apply across all ticket prices for Wales' clash with the Pumas, priced at £30 and £20 for adults; £15 for the under 18s enclosure and £70 for a family of four. For example, two families (4 adults and 4 children) will be able to enjoy the game for less than £10 per person.
Fans can take advantage of this sizzling summer offer online at www.wru.co.uk/tickets or by calling the ticket hotlines 08442 777 888 or 02920 230130.
WRU Head of Sales and Marketing Craig Maxwell said: "Wales versus Argentina is the final match of Wales' summer internationals before they head to New Zealand and the WRU is following the example of other rugby nations by offering two for one tickets to ensure that all Welsh fans get behind their team ahead of the Rugby World Cup.
"This summer will provide a feast of world class rugby action for fans and with a traditional and family-friendly 2.30pm kick-off announced across all fixtures, we've put a clear focus on families with our ticketing strategies.
"For the game against Argentina we are delighted to extend the two for one offer to the popular family pass as well as individually priced tickets and hope that families of rugby supporters take advantage of this great day out and give a rousing send-off to their national team."
Fans that have already purchased their tickets will be sent their free tickets in the post to accompany their original purchase.