Elections to Castlereagh Borough Council were held on 15 May 1985 on the same day as the other Northern Irish local government elections. The election used three district electoral areas to elect a total of 21 councillors.
<small>Note: "Votes" are the first preference votes.</small>
|- class="unsortable" align="centre" !rowspan=2 align="left"|Ward ! % <br /> !Cllrs<br /> ! % <br /> !Cllrs<br /> ! %<br /> !Cllrs<br /> ! % <br /> !Cllrs<br /> !rowspan=2|Total<br />Cllrs<br /> |- class="unsortable" align="center" !colspan=2 bgcolor="" | <span style="color:black;">DUP</span> !colspan=2 bgcolor="" | <span style="color:black;">UUP</span> !colspan=2 bgcolor="" | <span style="color:black;">Alliance</span> !colspan=2 bgcolor="white"| <span style="black;">Others</span> |- |align="left"|Castlereagh Central |bgcolor="#D46A4C"|58.2 |bgcolor="#D46A4C"|4 |19.6 |2 |20.5 |1 |1.7 |0 |7 |- |align="left"|Castlereagh East |bgcolor="#D46A4C"|46.2 |bgcolor="#D46A4C"|3 |31.9 |3 |18.1 |1 |3.8 |0 |7 |- |align="left"|Castlereagh South |bgcolor="#D46A4C"|40.1 |bgcolor="#D46A4C"|3 |35.5 |3 |17.7 |1 |6.7 |0 |7 |- class="unsortable" class="sortbottom" style="background:#C9C9C9" |align="left"| Total |48.0 |10 |29.0 |8 |18.8 |3 |4.2 |0 |21 |-
1985: 4 x DUP, 2 x UUP, 1 x Alliance
1985: 3 x DUP, 3 x UUP, 1 x Alliance
1985: 3 x DUP, 3 x UUP, 1 x Alliance