Reese has not been back in her sequin two-piece since last summer, when the franchise celebrated its 15th anniversary.
The star revisited her famous wardrobe from the films, appearing not to have aged a single day since she played the bubbly socialite.
On Monday, Deadline reported that much of the original creative team would be back on board for the third installment of Legally Blonde.
Writers of the first film, Kirsten 'Kiwi' Smith and Karen McCullah, are in talks to write the new movie.
Marc Platt, who produced the original, will return along with Platt Productions president Adam Siegel.
As well as starring, Witherspoon will co-produce under the banner of her company Hello Sunshine.
The original comedy, about a woman who goes to Harvard law school to win back the affections of her ex-boyfriend, was released in 2001 and the sequel Legally Blonde 2: Red, White and Blonde, followed in 2003.
In the second film, Elle heads to Washington D.C. to help pass a bill to ban animal testing.
A director has not yet been selected. Robert Luketic helmed the original and Charles Herman-Wurmfeld directed the follow-up.
The first movie grossed $141 million worldwide on an $18 million budget, and the sequel brought in $124 million on a $45 million budget.
The plot is being kept under wraps but Deadline reports that it will be in the spirit of the first film and be more about female empowerment.
Witherspoon is currently working on the second installment of HBO series Big Little Lies.
This time round Meryl Streep is joining the cast which also includes Nicole Kidman, Laura Dern and Shailene Woodley.
The last season won a Golden Globe for Best Television Limited Series or Motion Picture Made for Television.
Steep is playing Mary Louise Wright, the mother of Alexander Skarsgard's character Perry Wright. Her character arrives in Monterey searching for answers after Perry's death at the end of season one.
