Steele latched onto Alan White's huge clearance, controlled the ball superbly and beat Matthew Clarke before slotting home from 16 yards.
The O's were well worth their interval lead but Darlington hit back in the second-half - however the home side defended well to put a dent in the Quakers' promotion push.
It was Steele's 12th league goal of the season - but his first since the start of November - as Orient threatened to run riot at the start.
Darlington goalkeeper Sam Russell was their first-half hero as he made two smart stops to deny Daryl McMahon and Andy Scott before Orient made the all important break through after 26 minutes.
The home side almost added a second when defender Gaby Zakauni headed just over before the in-form Russell denied Scott as Orient continued to press.
The promotion-chasing visitors failed to produce a single shot on target during the entire first-half, and after the break the game looked likely to follow a similar pattern as Orient continued to press the accelerator.
Stand-in skipper Michael Simpson fired over and then Matt Lockwood saw a drive from 20 yards skip just past the post.
But as the game progressed Darlington became more of a threat as former Celtic star Bobby Petta stamped his authority on the game.
The visitors enjoyed plenty of possession, but they failed to really test Orient keeper Lee Harrison.
The home side looked dangerous on the break and the impressive White, a tower of strength at the heart of the home rearguard, headed a cross from O's sub Efe Echanomi just wide at one end and then scrambled the ball off the line at the other as the visitors almost snatched an 83rd minute leveller.
But it was too little, too late from Darlington as Orient took the points to keep their season alive.