Williams is among a bevy of former internationals in the BBC presenting team which also includes ex-England and Lions midfield back Jeremy Guscott, Welsh legend Jonathan Davies, ex-England players Mike Tindall, Brian Moore and Lewis Moody, Ireland's Keith Wood, Brian Moore and Frenchman Thomas Castaignede.
The BBC team will be led by veteran broadcaster John Inverdale and Gabby Logan with Williams and company providing expert analysis. The commentary team will be led by former Wales No. 8 Eddie Butler.
Their ITV rivals have also assembled a stellar line-up of former internationals heading by Jonny Wilkinson, Gareth Thomas and Brian O'Driscoll. Former Scotland and Lions coach Sir Ian McGeechan is also a key presenter.
Fitzpatrick has long been a part of ITV's rugby coverage team and worked for the network at last year's World Cup in England and Wales. Brooke has previously worked for the BBC.
But neither appears to be wanted for the Six Nations with Williams, once known as 'Comical Ali' for his occasionally bizarre press conferences during his playing career, is the only New Zealander involved, although three of the competing national teams are coached by Kiwis in Wales (Warren Gatland), Scotland (Vern Cotter) and Ireland (Joe Schmidt).
The 2016 Six Nations marks the start of a six-year deal between the BBC and ITV that will see the matches shared between the broadcasters on television and online.
The BBC will have exclusive television coverage of four of the first six games from the tournament including the Calcutta Cup game between Scotland and England from Murrayfield.
Meanwhile, on ITV, Mark Pougatch leads the broadcast team with Lawrence Dallaglio and Jason Robinson - both members of England's victorious Rugby World Cup 2003 team, along with their coach Sir Clive Woodward - will join Wilkinson, Thomas and O'Driscoll in their line-up.
ITV will show both of England's home games.
More than 24million people watched the BBC's coverage of last year's Six Nations.
- staff reporter and Daily Mail