The hosts claimed a priceless victory to end their losing streak and move above Wigan, sixth before this match, on points difference with just two games to play.
Broncos now face games against Salford and Widnes while the Giants, who still must play the Warriors, now need a minor miracle to extend their season.
The visitors were the in-form team going into the match, and they also had a better recent head-to-head record - but it was Broncos who started strongly.
They thought they had claimed a try after just two minutes when Luke Dorn delicately chipped towards the try line as the Giants defence reeled, but the television replays revealed Steve Trindall did not ground the ball.
Former Broncos favourite Chris Thorman threaded a penalty to give the Giants an early advantage. But seconds later Nick Bradley-Qalilawa scored a stellar try after some quick handling broke down the visitors? rearguard. Paul Sykes pulled the conversion kick wide.
Brad Drew's forward pass denied the Giants an immediate response with the Broncos defence breached, although Thorman restored the lead with two kicks for goal.
Broncos though were playing the more expansive game and deservedly moved ahead with their second try.
Another slick passing move broke down Huddersfield and Feleti Mateo?s reverse pass was gathered by full-back Zebastian Lucky Luisi for a crucial score.
The half ended on a fiery note when Broncos enforcer Solomon Haumono took exception to an Eorl Crabtree high tackle and received a stern warning from the referee for his act of retaliation.
Huddersfield finally found the required level after the break, taking the lead when Stanley Gene neatly side-stepped a flailing Danny Williams tackle before releasing Thorman for a try he also converted.
But the Giants will forever regret their failure to make the most of the domination to follow that score.
Jon Wells scored his ninth - and most important - try of the season to put the Broncos back ahead, although another refereeing decision seemed to go in London?s favour after Sykes? final pass appeared forward.
Nerves crept into both sides games in the dying minutes with a series of knock-ons and dropped balls meaning the referee?s whistle constantly punctuated proceedings.
However, London always looked like hanging on to their most important victory of the season.
London: Lucky Luisi, Wells, Smith, Sykes, Bradley-Qalilawa, Hopkins, Dorn, Trindall, Highton, Armour, Haumono, Ablett, Mbu. Replacements: Williams, Tookey, Lolohea, Mateo.
Huddersfield: Reilly, O'Hare, Evans, De Vere, St Hilaire, Thorman, March, McDonald, Drew, Crabtree, Nero, S. Jones, Gene. Replacements: Gannon, Grayshon, White, Jackson.
London (10) 16. Tries: Bradley-Qalilawa, Lucky Luisi, Wells. Goals: Sykes 2.
Huddersfield (6) 12. Tries: Thorman. Goals: Thorman 4.
Referee: Richard Silverwood (Dewsbury) Att: 2,877Like