Ivorian winger Gradel struck in the 25th and 70th minutes to take his season's tally to six as Leeds stretched their unbeaten league run to nine matches and climbed to within three points of the Londoners, who lost their second successive match.
Cardiff's home clash with Burnley was postponed and Swansea lost at Sheffield United, leaving rampant Leeds to take full advantage against Rangers, who lost for the first time this season when Watford won 3-1 at Loftus Road eight days ago.
Simon Grayson's side were always in control and after a scrappy opening period played the better football against this season's early pacesetters in the Championship.
Leeds were unchanged from the side that beat Burnley last week, while defender Bradley Orr and Rob Hulse returned for QPR.
The visitors twice threatened in the opening exchanges, with Orr firing over the crossbar from inside the penalty area and then former Leeds striker Hulse seeing his header saved by Kasper Schmeichel.
Leeds were dealt an early blow when centre-half Alex Bruce was forced off through injury and replaced by Leigh Bromby, but almost broke the deadlock themselves as Luciano Becchio's header was turned away at full stretch by QPR goalkeeper Paddy Kenny.
Snodgrass then pulled his shot wide as Leeds built momentum and, although Adel Taarabt went close for the visitors, the home side took the lead in the 25th minute when Snodgrass crossed from the right and Gradel slammed home his second goal in as many games into the bottom corner from six yards.
QPR responded through Clint Hill's header, which was blocked by Leeds defender Neill Collins, and Kaspars Gorkss, who volleyed the ball wide when well placed in the area.
Tempers flared following mistimed tackles from Leeds midfielder Bradley Johnson and Rangers defender Hill, while home right-back Paul Connolly and Orr were booked by Stockport referee Scott Mathieson at the end of the first period.
Fitz Hall replaced Hill at half-time and QPR striker Jamie Mackie's shot was blocked by Collins soon after the restart, but Leeds went straight back on the offensive.
Becchio's blistering drive from 20 yards was brilliantly saved by Kenny and Gradel went close from another Snodgrass cross in the 53rd minute.
But Leeds were not to be denied in the 70th minute when George McCartney set Gradel scampering forward on the counter-attack.
The Leeds winger beat his marker and raced into the visitors' penalty area before burying an emphatic finish into the bottom corner.
Kilkenny volleyed just wide soon after as Leeds threatened to extend their lead and Jonny Howson forced Kenny into another fine save with a 20-yard effort.
Snodgrass and Becchio, whose header was cleared by Gorkss, also went close for the home side, who were full of confidence and ran out convincing winners in front of a crowd of 30,000 at Elland Road.