Ibrahimovic took his MLS goals tally to three in three games after heading home a cross from former England and Chelsea star Ashley Cole on 45 minutes.
The former Manchester United and Sweden striker had made a dramatic arrival in MLS earlier this month, scoring twice on his debut in a 3-2 win over Los Angeles FC.
But Ibrahimovic had found the going harder last weekend as the Galaxy were well-beaten by Sporting Kansas City in a 2-0 loss.
However, the MLS giants responded with a battling performance against Chicago at a rainswept Toyota Park on Saturday.
Ibrahimovic's goal came on the stroke of half-time, when the forward glided into space in the area to meet Cole's cross from the left flank with a perfectly placed header that gave goalkeeper Richard Sanchez no chance.
Ibrahimovic was replaced ten minutes from time as the contest grew increasingly niggly.
Three Galaxy players — Romain Alessandrini, Perry Kitchen and Cole — were cautioned along with Fire players Brandon Vincent and Alan Gordon.
The win lifts Galaxy into second place in the Western Conference standings with ten points from six games.