The new features a refreshed homepage, integrated film and photo galleries, an enhanced search engine and a special RSS-type feed to tell supporters about breaking news.
The charity is using the new website to promote two upcoming demonstrations taking place in the capital.
The event on February 28, which will feature a number of keynote speakers, seminars and a rally will be followed by the march, a five-day demonstration leading up to the G20 summit on April 2.
Both demonstrations are aimed at raising the profile of global poverty, climate change and human rights.
Corin Pearce, technology manager for War on Want, said: "The new year has seen us gather momentum through initiatives such as a report on exploited wine workers and planned campaign events.
"With a rising profile as the UK's foremost charity tackling the causes of world poverty, the new website can win even more public backing for our work."
War on Want's old website helped the charity place among Britain's top five charities in a poll conducted by magazine.