The Scottish midfielder struck a quite stunning 35-yard dipping shot midway through the second half to overcome a dogged Birmingham.
Ellen White had earlier registered her first goal for City after her summer move from Birmingham only for the visitors to level on the hour.
But Weir’s amazing effort saw City secure a second Group C win and sent us into the international break on a positive high after our run of three straight losses.
City showed their collective confidence hadn’t been dented by our tough recent run, as we took the game to the visitors from the off.
On 10 minutes a fine long ball from Megan Campbell found Ellen White who powered up the left flank before her inviting curling cross was a metre away from the onrushing Pauline Bremer.
More good work on the left channel from Campbell found Hemp and from her inviting cross, Beckie – deployed in the unfamiliar role of right back - saw her snap-shot just miss the target.
Midfielder Caroline Weir then produced a superb twist and turn before threading a precise through-ball to Bremer whose shot was parried by Birmingham keeper Hannah Hampton.
Though City monopolised both territory and possession Birmingham were however a threat on the counter and keeper Ellie Roebuck needed to be alert on the half hour to gather Rachel Williams’ 20-yard low drive.
White was then denied a first City goal by a timely block from Harriet Scott as the striker prepared to meet Stanway’s delivery.
With the game opening up, Roebuck was called into action again on 35 minutes to keep out Brianna Visalll’s drive after the City defence was bisected by Williams’ well-timed pass.
Five minutes from the break City produced their best move of the half. The impressive Campbell and White linked to great effect and the England striker showed great vision to find the waiting Bremer lurking 10 yards out.
However, the German international’s looping header arced just over the target.
With space opening up, Roebuck then earned her spurs once again producing a superb dive to tip away Staniforth’s powerful goalbound effort.
City stepped up the intensity and the goal their efforts merited arrived on 50 minutes as White recorded her first goal for the Blues – and against her former team-mates.
Hemp was the architect powering past Sarah Mayling on the left wing and from her low cross, White insantly fired the ball into the roof of the net to delight of the home fans before producing her trademark spectacles celebration.
Birmingham though were still dangerous and, after Beckie had produced a goal-saving tackle on Grant, the visitors levelled affairs on the hour.
Scott found space on the right before picking out the unmarked Williams in the box who headed home from six yards.
City though weren’t to be denied and a moment of sheer brilliance from Weir restored our advantage on 68 minutes.
There seemed little danger as the Scot found the ball just inside the Birmingham half.
But after marauding forward she unleashed a remarkable dipping shot from 35 yards which arrowed over Hampton into the roof of the Birmingham net.
How we lined up
Ellie Roebuck was in goal with Megan Campbell, Gemma Bonner, skipper Steph Houghton and Janine Beckie deployed in defence. Jill Scott, Caroline Weir, Lauren Hemp and Georgia Stanway formed the midfield quartet with Pauline Bremer and Ellen White the strike spearhead.
What it means
City have six points from three games in Group C and share top spot with Manchester United and Birmingham with Cushing's squad having one group game remaining.
With the November international break following today’s game, City are not in action again until Sunday, November 17 when we entertain West Ham in the FA Women’s League. Kick-off at the Academy Stadium is 12.30pm GMT.