The 24.2km trails start and finish at the Look Out Discovery Centre, in Nine Mile Ride, Bracknell, and provide a range of routes for cyclists of all abilities.
The trails, set in 1,000 hectares of the forest, have been renovated by the Crown Estate, which owns the land.
The estate's chairman Sir Stuart Hampson and chief executive Alison Nimmo cut a big mountain bike cake to celebrate the opening of the trails to the public on Tuesday.
Ms Nimmo, said: "It's great to be here today to open these fantastic new cycling trails.
"Thousands of people visit
us here on the Windsor Estate
each year and Swinley Forest has become a mecca for cyclists. We hope our investment will reduce the number of serious accidents, widen the visitor offer and balance this with protecting the forest's delicate ecology."
It is estimated up to 170,000 cyclists use the site each year. The new routes have been classified according to International Mountain Bike Association industry standards, allowing riders to pick a suitable track. It is hoped cyclists will stick to the formal routes which will help protect other parts of the forest - designated a Special Protection Area by Natural England.
Chief forester John Deakin said he had received positive feedback from cyclists on the new routes.
He said: "Our ambition from the outset was to provide a high quality recreational facility in Swinley Forest, while working with partners like Natural England to protect the important habitats and natural features that make the Forest unique.
"The network achieves both of these aims and I would encourage anyone with the opportunity to go out and enjoy the new routes. "
Regular cyclist Ben Pinnick, from Crowthorne, said: "The programme of creating a sustainable and manageable facility for cyclists using Swinley Forest has been extremely successful. It has been very well received by riders, especially families and younger riders using the forest for the first time.
"With a good diversity of easy and more challenging trails, it shows that despite the lack of real hills, it is possible to provide something for all riders, abilities and styles if done properly."