Archbishop Desmond Tutu praised Maathai as a true "visionary African woman" and called her a "leading voice on the continent."
He said: "Professor Maathai introduced the idea of women planting trees in Kenya to reduce poverty and conserve the environment," in a statement released via his office.
"At last count, the Green Belt Movement she helped to found had assisted women to plant more than 40 million trees. She understood and acted on the inextricable links between poverty, rights and environmental sustainability. One can but marvel at her foresight and the scope of her success. She was a true African heroine," the statement continued.
"Our condolences go to Professor Maathai's family, to the people of Kenya, and to the countless women (and men) across Africa and the world to whom she was an inspiration."
"She will be remembered as a committed champion of the environment, sustainable development, womens' rights, and democracy. Her contribution to all these causes will forever be celebrated and honored," he said.
"Wangari was a courageous leader. Her energy and life-long dedication to improve the lives and livelihoods of people will continue to inspire generations of young.
"Her award of the Nobel Peace Prize in 2004, the first to be bestowed upon an African woman, rightly underscored the important nexus in her work between sustainable development, peace and human security."
Tanzania's President Jakaya Kikwete was among the first world leaders to celebrate the professor's life.
"Rest in peace Dr Wangari Maathai. A great woman, an inspiration for many women across Africa, a magnificent visionary and embodiment of courage," President Kikwete said on Twitter.
Former U.S. vice president Al Gore also paid tribute to Maathai who he said "overcame incredible obstacles to devote her life to service—service to her children, to her constituents, to the women, and indeed all the people of Kenya-- and to the world as a whole."
In a statement, he said: "Wangari was a warm and devoted mother and I send my condolences to her family. She worked tirelessly both as an elected Member of Parliament and an Assistant Minister for Environment and Natural Resources. She forged new ground for women in Kenya helping shatter what we would call the 'glass ceiling' in the United States."
A spokesman for the Nelson Mandela Foundation said in a statement that Maathai has left a "lasting legacy in greater awareness and work in protecting our environment and the world."
The statement praised Maathai for a speech she delivered in 2005 at the Third Nelson Mandela Annual Lecture, while she was Deputy Minister of Environment in Kenya.
She will be remembered as a committed champion of the environment, sustainable development, women's rights, and democracy
"We need people who love Africa so much that they want to protect her from destructive processes," she said in her address.
"There are simple actions we can take. Start by planting 10 trees we each need to absorb the carbon dioxide we exhale. Get involved in local initiatives and volunteer your time for services in your community," she continued.
A spokesman for the Kenyan government said the death of Maathai was "a huge loss to the country, Africa and the whole world" and had left a "gaping hole that will be difficult to fill."
He said Maathai had been receiving treatment for ovarian cancer at the Nairobi Hospital for the past year.
He added: "Prof. Wangari Maathai brought meaning to the words peace and environment. She made the world understand that water, trees, and protection of the environment helps us achieve real peace.
He continued: "She was deserving of the Nobel Peace Prize because she taught all of us the importance of respecting our planet and each other. Her passion, dedication and focus became a beacon to be emulated by millions."
Bineta Diop, Founder of Femmes Africa Solidarite, an organization working on issues of gender, peace and development, remembered Maathai as someone who risked her life for ordinary people.
We need people who love Africa so much that they want to protect her from destructive processes
"Africa has lost today one of its greatest daughters. Wangari was the champion of the environmental cause, to which she brought the attention of the Continent when nobody was talking about this great challenge. She worked tirelessly for the rural women, demanding African leaders to address climate change," she said.
Diop said she would continue to inspire generations to come: "We are sure that the young women and men she mentored are ready to continue her fight for climate justice."
Meanwhile, tributes flooded in on social networking sites Facebook and Twitter. Maathai was trending worldwide on the micro blogging website as people from around the world remembered how she had touched their lives.
Ann Pettifor, from the New Economics Foundation tweeted: "Wangari was my heroine. Jubilee 2000's African leader and did great work for Kenya's debt."
Another tweeter, Lorde Sirm, wrote: "A symbol of hope, dreams in a world full of green rest in peace."
There were also calls for her to receive a state burial on Twitter with user, KGitonga, tweeting: "We failed to honor her when it mattered. Let her rest in humility like she lived."
There were also calls on Facebook for her work to continue, one user, Catherine Gitonga wrote: "May we honor her by planting as many trees as we can so that her legacy may live on and we may fulfill all that she fought for. Rest in peace knowing that your contribution to Kenya will forever be remembered."
On Facebook, Lorot Saleml wrote: "I refuse to believe that Mama is dead. She lives among us. She lives in my poems. She lives in the trees. She is the air I breath. Her soul is in Uhuru park. Her soul is roaming all over the world. My mama still lives on."
Eoghan Macguire contributed to this report.