Soares, on loan from Stoke, opened the scoring at Kilmarnock after latching on to Leigh Griffiths' throughball.
O'Donovan extended the advantage when the loanee from Coventry cracked a stunning 30-yard effort in the second minute of the second half.
Soares grabbed his second goal after 65 minutes when he connected with Griffiths' cross to heap further misery on the Rugby Park side.
Dean Shiels' bending free-kick restored some hope for Kilmarnock with eight minutes remaining, however the visitors survived some late pressure to claim the points.
The first 10 minutes of the match lacked any real pattern.
The home fans then breathed a sigh of relief as Cammy Bell did well to recover Ben Gordon's wayward back-pass, with Griffiths ready to pounce on any error.
Hibs opened the scoring after 17 minutes with the first scoring opportunity of the match.
Griffiths' threaded pass caught the Kilmarnock defence on their heels and Soares controlled brilliantly before slotting beyond Bell.
Griffiths fired a shot just over a minute later as the visitors looked to extend their lead.
The hosts managed their first attempt on the Hibernian goal after 25 minutes when Michael Nelson's effort was almost deflected beyond Graham Stack by the back of James Dayton.
Dayton was the first player to pick up a yellow card after hauling down Pa Kujabi as he raced through on goal and from the resulting free-kick George Francomb struck the top of Bell's crossbar.
Poor defending almost caused led to Hibernian extending their lead when Isaiah Osbourne's header caught out the home defence.
Griffiths sped through on goal and forced Bell into a fantastic stop before Soares headed over from the rebound with the goal gaping.
Bell denied Griffiths again minutes later when a hopeful clearance left the unmarked striker to charge through on goal, however Bell was more than equal to his stinging effort.
The visitors extended their lead just 90 seconds into the second half.
A loose ball broke to O'Donovan who turned and fired a spectacular effort over Bell and into the net.
Kilmarnock went close on the hour mark when Nelson saw his header cleared off the line by Francomb after rising to meet Shiels' corner.
The home fans were growing increasingly frustrated at their teams' inability to retain possession and but for a poor pass from Kujabi, Griffiths could have had the opportunity to race clear through.
Soares heaped more misery on Kilmarnock after 66 minutes when he lashed home his second goal of the afternoon after another pinpoint delivery from Griffiths.
Kilmarnock gave their fans something to cheer about with eight minutes remaining when Shiels' free-kick left Stack with no chance.
Paul Heffernan's header was deflected past the post as the home side looked to stage an unlikely comeback and Paul Hanlon then had to be alert to clear Lee Johnson's dangerous cross.
The home side's late pressure was all in vain however, as the visitors comfortably saw out four minutes of injury-time to claim a vital three points.