you should just hav to move your left join outside the derived table (V) as such

SELECT

pr2.presenterName,

V.PresenterID,

V.VoteFor,

CAST(V.VoteFor * 1.00 / @TotalVotes as Decimal(3,2)) as VotePercentage

FROM (--get votes for presenter

SELECT

pr2.PresenterID,

SUM( CASE WHEN VoteFor = 1 THEN 1 WHEN VoteAgainst = 1 THEN -1 ELSE 0 END) as Votes

FROM dbo.tblCompWeek_02 q

WHERE pr2.PresenterGender=@Gender

GROUP BY

q.PresenterID,pr2.PresenterID,pr2.PresenterGender) V

left outer JOIN dbo.tblPresenters pr2

ON v.PresenterID = pr2.PresenterID