ST KILDA has extended coach Alan Richardson's contract for a further two seasons, with the deal set to be announced at Friday night's best and fairest.

Richardson was due to come out of contract at the end of next season, but both the coach and the Saints have long been keen to extend their partnership.

It is understood negotiations have been smooth, with detailed talks starting at the end of the Saints' season.

The deal will make the 52-year-old the club's longest serving coach in more than four decades if he serves his full term to the end of 2020.

Richardson will match Ross Lyon's five seasons as St Kilda coach next year and would equal Grant Thomas's six seasons as senior coach in 2019.

His seventh season in charge would be most since coaching great Allan Jeans ended his 16-year run in 1974.

Richardson took over from Scott Watters at the end of the 2013 season and improved the Saints' record in each of his first three years in charge, leading the club to a 12-win season in 2016.

The Saints fell away in 2017, winning 11 games to finish 11th and losing five of their last seven games in a disappointing end to what shaped as a promising season.

Richardson was one of four coaches coming out of contract at the end of next season, alongside Don Pyke (Adelaide), premiership coach John Worsfold (Essendon) and Damien Hardwick (Richmond).

Chris Fagan (Brisbane Lions), Nathan Buckley (Collingwood), Chris Scott (Geelong), Alastair Clarkson (Hawthorn), Simon Goodwin (Melbourne), and Adam Simpson (West Coast) have contracts until the end of 2019.

Lyon (Fremantle), Leon Cameron (GWS), John Longmire (Sydney), Brad Scott (North Melbourne) and Luke Beveridge (Western Bulldogs) are locked away until the end of 2020.

New Gold Coast coach Stuart Dew has signed an initial three-year deal through to 2020, while Port Adelaide last month extended coach Ken Hinkley through to the end of 2021.

Carlton coach Brendon Bolton is a permanent member of staff at the club, with no contractual end date but protection for both the coach and the Blues should they part ways.