The former Hearts, Celtic and Aberdeen midfielder took over the English League Two side in the summer having led Cove Rangers to the Championship.
Saturday’s 2-0 defeat at Sutton United left the club second bottom of the fourth tier with four points and no wins from nine games.
Hartley undertook an extensive recruitment drive, signing 17 players, many from Scottish football or with experience of the SPFL.
Euan Murray, Jake Hastie, Jack Hamilton, Mouhamed Niang, Reghan Tumilty, Chris Maguire and Kyle Letheren were amongst those signed.
A club statement read: “Hartlepool United can today confirm that they have parted company with manager Paul Hartley and assistant manager Gordon Young.
“A decision was taken to make a change with the club currently sitting second from bottom in League Two and without a league win so far this season.
"A further update on succession plans will follow in due course.”