Brown’s side kept clean sheets in every game as they recorded seven straight league victories – including a 1-0 win at rivals Bury – to move into the automatic promotion place.
Burton Albion’s Jimmy Floyd Hasselbaink joins him on the list after four wins and two draws guaranteed their place in League One next season.
Shrewsbury will join Burton in the third tier of English football after Micky Mellon guided them to five wins from six matches, again, like Southend, without conceding a goal.
The highlight of the run, which earned the Scot a nomination on the list, was a 4-0 victory over play-off chasing Exeter City.
Stevenage boss Graham Westley completes the line-up after his side cemented a place in the end-of-season play-offs after four one-goal victories and two draws in their six matches.
In Sky Bet League 1, Paul Cook is on the shortlist after he drove Chesterfield on to secure the final play-off spot with three wins in four games at the start of the month, including a 6-0 success over relegation-threatened Colchester United.
Steve Cotterill makes the panel for a fourth successive month, and sixth of the season, after his Bristol City side secured the title after remaining unbeaten in six matches during the month.
Preston North End remain in the automatic promotion places after collecting 15 points from seven unbeaten games, a run which has kept MK Dons one point back and earned manager Simon Grayson his spot among the nominees.
MK Dons can yet deny Preston a place in the Championship and boss Karl Robinson is added to the shortlist after watching his team take 19 points from a possible 21 – with a 20-3 goal difference – while winning five of those seven games by at least two goals.
In the Championship, Bournemouth boss Eddie Howe makes the four-man shortlist after securing promotion to the top flight of English football for the first time in the club’s history.
Howe’s side took 14 points from six games to close within one point of leaders Watford ahead of their final game of the season against Charlton at the Valley.
Watford boss Slavisa Jokanovic, whose table-toppers can clinch the Championship title with victory at home to Sheffield Wednesday on Saturday, joins Howe on the list after bagging 16 points from a possible 18 during the month.
Norwich boss Alex Neil makes the line-up despite seeing his side’s challenge for automatic promotion falter during the past few weeks.
A home defeat to Middlesbrough and a draw away at Rotherham, after leading for much of the game, means the Scot – whose side bagged 13 points from a possible 18 – will have to settle for a place in the play-offs.
Completing the list is Birmingham City boss Gary Rowett who has guided his team to a top-half finish in the Championship table after collecting 13 points from the 21 on offer.
Rowett, who has become a huge favourite with the St Andrew’s faithful, was nominated earlier in the season for a League Two equivalent during his time in charge at Burton Albion.
The winners of the Manager of the Month awards will be announced on Friday, May 1.