The leading garden designer and columnist’s company has been appointed by engineers ARUP, which is developing the idea alongside Heatherwick Studios and Transport for London.
The pedestrian bridge is planned to cross the River Thames between Temple and the South Bank and would feature woodland and wildflowers, blossom in the spring and a Christmas tree in the winter.
Pearson said: "'We are honoured and delighted to have been selected to provide landscape design services for this exciting project. Our studio is close to this part of the river and the garden bridge will provide another, more human, means of crossing the Thames to the cultural hub of the South Bank.
"We are very much looking forward to developing our ideas for planting alongside Thomas and his team and helping to bring this visionary project to fruition."
Heatherwick was commissioned by Transport for London to look at a new foot crossing.
The plan is being championed by Joanna Lumley who said: ""This garden will be sensational in every way: a place with no noise or traffic where the only sounds will be birdsong and bees buzzing and the wind in the trees, and below the steady rush of water.
"It will be the slowest way to cross the river, as people will dawdle and lean on parapets and stare at the great cityscapes all around but it will also be a safe and swift way for the weary commuter to make his way back over the Thames.
"I believe it will bring to Londoners and visitors alike peace and beauty and magic."