Samoa completed the line-up for the 2008 World Cup in Australia when they beat Lebanon 38-16.
They will now line up alongside Ireland and Tonga in Group C of the 10-team tournament taking place next October and November.
Scotland, who secured their place with a two-legged aggregate win over Wales, are in Group B with Fiji and France.
England, Australia, New Zealand, France and Papua New Guinea were automatic qualifiers.
Here's how qualifying unfolded.
Tonga became the first team to qualify from the group stages after beating Samoa 18-10 in the final match of the Pacific group.
Fiji also go through to the main draw as runners-up.
Samoa, who beat Fiji and the Cook Islands in earlier group matches, lost out on automatic qualification on points difference but went on to qualify through the repechage.
Tonga 56-14 Cook Islands
Samoa 30-28 Fiji
Fiji 30-28 Tonga
Samoa 46-6 Cook Islands
Fiji 40-4 Cook Islands
Tonga 18-10 Samoa
The United States beat Japan 54-18 to qualify for the repechage.
The two teams were the only ones left in the group after South Africa and the West Indies withdrew.
Unfortunately for the US, they lost out to Samoa in the first round of the repechage.
USA 54-18 Japan
Scotland and Ireland topped their groups to earn their place at the World Cup finals.
Wales and Lebanon went through to the repechage but failed to progress to the main draw.
Russia 40-14 Netherlands
Georgia 45-10 Serbia
Georgia 57-16 Netherlands
Russia 44-6 Serbia
Netherlands 38-26 Serbia
Russia 24-0 Georgia
Wales 14-21 Scotland
Scotland 16-18 Wales
Russia 12-50 Ireland
Lebanon 22-8 Russia
Ireland 18-18 Lebanon
Ireland 58-18 Russia
Russia 0-48 Lebanon
Lebanon 16-16 Ireland
Samoa sealed the final qualifying spot by beating US and then Lebanon.
Game One: Wales 26-50 Lebanon
Game Two: USA 10-42 Samoa
Game Three: Samoa 38-16