The Shropshire Wildlife Trust has bought the acre of land at The Mount after a two-year campaign which brought in more than 430 donations and the backing of Sir David Attenborough.
They plan to restore the woodland and open it the public.
The land includes a path where Darwin walked each morning as a child.
His birthplace at The Mount is now private housing and much of what was the garden has been built on.
But the charity has now secured the remaining one acre plot which runs by the River Severn, part of which was known as The Thinking Path.
Such was its importance to Darwin that he created a similar route when he moved to Kent with his wife, Emma.
The Shropshire Horticultural Society and Harper Adams students were among the contributors to the campaign.
Officials from the charity now believe that the path will become "a cherished corner of the world".
Colin Preston, director of Shropshire Wildlife Trust, said: "No other part of Darwin's childhood home is accessible to the public so, when we were offered the chance to buy this slip of woodland next to the river, we were thrilled at the opportunity."
The trust plans to give guided tours of the historic woodland to schools, and to encourage children to see the natural world through Darwin's eyes.
The campaign not only brought in donations from within the county but from London and even from America.
Sir David Attenborough also gave his support, calling the campaign a "once-in-a-lifetime chance to put people in touch with this extraordinary man and his discoveries".
The deal comes just in time for Shrewsbury's annual Darwin festival, which will take place on February 15 and 16, and will include a guided tour of the garden.
For more information on events call (01743) 284280.