The money, awarded by WREN's FCC Community Action Fund, will pay for the refurbishment of the park's play area including resurfacing and the supply and installation of new equipment.
The grant was made following a successful bid by South Kesteven District Council, which owns the park, and Dysart Park Action Group.
The Action Group raised almost £6,000 in match funding to support the bid, mainly through its annual Summer Fun Days. At the 2018 event refurbishment options were on show and visitors voted for their favourite.
SKDC Cabinet Member for Retail and Visitor Economy, Cllr Nick Robins, said the investment would make a huge difference to the park, which is visited by around 30,000 people a year.
"It's fantastic that WREN has awarded this money. This is a very important community facility and the work will only add to its appeal," he said.
"This is just the start of work as SKDC is committed to investing further in not only Dysart Park, but all of the parks it owns."
WREN is a not-for-profit business that awards grants for community, biodiversity and heritage projects from funds donated by FCC Environment through the Landfill Communities Fund.
Cheryl Raynor, WREN's local grant manager said: "We are delighted to be supporting the Dysart Park refurbishment project and pleased that our funding will provide such a fantastic facility for children.
"WREN is always happy to consider grant applications for projects that make a difference to local communities and we're really looking forward to seeing this one take shape."
The park site was given to the people of Grantham in 1908 by Sir Lionel William John Manners, late Earl of Dysart. In his will he stated that the land should be used for recreation purposes only.
District councillors Michael Cook and Graham Jeal are members of the Action Group, while officers prepared the application for WREN funding.
Cllr Jeal said: Dysart Parkis a popular and well-used community park. The Action Group has worked hard over several years to deliver the Dysart Park Fun Day, which has generated the match funding resources for this redevelopment of the children's play area.
"I congratulate all those hard-working volunteers for this fantastic achievement and thank all those who have made the Fun Day such a success. I look forward to working with SKDC to continue investment in Dysart Park."
Lydia Gallaher, chairman of the Action Group, said: "The council support has been invaluable. It was recognised that areas of the park required improvement, with the play area being the start.
"Although money generated from the Fun Days has allowed for the purchase of park benches in the past, it is a welcome achievement for the Action Group, in partnership with the council, to be able to make more of an impact.
"The benefit to the community will be that families, especially those with young children, will soon be able to enjoy new and exciting play equipment, making the park an even more attractive place to visit.
"The Action Group has worked hard over the years to promote and improve the park. The successful WREN application and the new play equipment it pays for will make that hard work and dedication worthwhile."
The Action Group has eight volunteers, and is always on the lookout for more. It organises family events, including the Fun Day, and raises money to improve the park. The volunteers meet every four to six weeks with breaks in the summer and at Christmas.
"We attend the meetings to provide input in discussions about the park and its events and to support the work of the Action Group towards improving the park or laying on events," said Lydia.
"Volunteers are always welcome to join and play their part in helping to shape and develop what is a very popular park that hold a special place in people's affections."
Work on the play area is expected to start in March and take up to three weeks to complete.
Anyone interested in volunteering with the Action Group should email email@example.com
For more information about WREN funding contact Cheryl Raynor at firstname.lastname@example.org visit http://www.wren.org.uk/
Caption 1:Pictured in the park are, left to right, Action group members Cllr Mike Cook, Hannah Martin, Midge Cook (treasurer), Amy Taylor, Kate Mason, Sarah-Jane Tinkler (vice-chair), Lydia Gallaher (chair), and Cllr Graham Jeal.
Caption 2:New play equipment planned for the park, which will be installed by Wicksteed.