The Spaniard put an end to his nine-match barren run with a clinical strike from Emmanuel Adebayor's cross on 28 minutes to keep Spurs' top-four hopes alive.
Having taken just 10 points from the nine league matches that have immediately followed Europa League ties this season, Spurs built on the 3-1 win over Dnipro on Thursday with a hard-fought victory.
Tim Sherwood's men took the lead through Soldado after 28 minutes as the Spaniard found the net for the first time since December 29.
Strike partner Emmanuel Adebayor selflessly opted to play the Spaniard in before Soldado took a touch and fired the ball past David Marshall with the outside of his right boot.
It proved to be the only goal of the game as 19th-placed Cardiff - without an away league win since September - saw its relegation fears heightened.
Aaron Lennon, one of two Spurs changes, was quick to make an impact, providing a cross after just a minute that Soldado was only able to divert wide.
Craig Bellamy, making his return from a three-match suspension, then whistled a free kick over the crossbar before laying on an opportunity for Fabio, whose shot was well blocked by Michael Dawson.
Andros Townsend was next to threaten during an open first 15 minutes, forcing Marshall into action with a low, driven effort.
After seeing Dawson go close with a volley and a header from a corner, Tottenham continued to dominate possession and was soon rewarded.
Soldado showed his quality to latch on to Adebayor's pass, calmly control the ball and place it home to register his first goal of 2014.
Steven Caulker almost leveled against his former club, crashing a header against the crossbar from Bellamy's corner, and Declan John stung the palms of Hugo Lloris three minutes before the break to offer a reminder that Cardiff was still in the contest.
Lennon almost weaved his way through the visiting back line five minutes into the second half and continued to cause problems, drawing a foul from John just outside the penalty area.
Townsend tested Marshall with the resulting free kick and the goalkeeper denied substitute Harry Kane late on, although it mattered little as Cardiff failed to find a leveler.
Ole Gunnar Solskjaer's side, which visits bottom club Fulham on Saturday, remains three points off West Brom in 17th, having played a game more than Pepe Mel's men.
For Tottenham head coach Tim Sherwood, the win represents an ideal tonic ahead of Premer League clashes with London rivals Arsenal and Chelsea later this month, as well as a Europa League tie against Benfica.