New owner Ann Budge, who completed the purchase of the financially-stricken club last week, has acted quickly to restructure as Hearts prepare for life in the Scottish Championship next season.
Locke and Brown have both been told that their contracts, which were due to expire this summer, will not be renewed and former Hearts defender Robbie Neilson, 33, will be promoted to head coach from U20 coach.
The Edinburgh club were relegated after finishing bottom of the Scottish Premiership following a 15-point deduction for going into administration.
A ban on transfers saw Hearts' first-team squad reduced to largely inexperienced youngsters and they finished the season 12 points adrift at the foot of the Scottish Premiership table.
However, that has not saved Locke from losing his job within hours of Budge taking up the reins at Tynecastle.
Budge released a statement which read: "We know it may be an unpopular decision with some of you, but the board has decided that we cannot offer Gary Locke a new contract as manager, at the end of his current contract.
"Please believe me when I say this has been an enormously difficult decision to make. We all know the pressures that Gary and his assistant, Billy Brown, have worked under over the last year.
"They were set an almost impossible task, which they handled with dignity and determination. For that, we are all hugely grateful to both of them.
"Craig Levein will join the club with immediate effect and will assume total responsibility for everything to do with the playing side of the business.
"Robbie Neilson will take over as head coach for the first team and we will bring in a strong support team to work with Robbie."
Hearts later confirmed Jamie Hamill, Jamie MacDonald, reserve goalkeeper
Mark Ridgers, midfielder Callum Tapping and defender Dylan McGowan would all be allowed to leave at the end of their contract this summer.
But there was no mention of Ryan Stevenson, whose release had also been rumoured - he has one year remaining on his contract and rejected offers to leave in January.
Jason Holt, Jamie Walker, Dale Carrick, Jack Hamilton, Brad McKay and David Smith will remain at the club for next season while negotiations are under way with Sam Nicholson and Gary Oliver.