The phrase "election victory" refers to winning an election. It means that a person or a political group has secured more votes than their opponents and emerged as the winner in the election. Full definition
A couple of candidates fell short in 2014 primaries and are trying to push through to general election victories in 2016. (rollcall.com)
The unexpected Conservative election victory of 2015 transformed British politics. (theguardian.com)
Even so at the start of a reign a prime minister has an authority he or she will only possess again if they win a big election victory. (totalpolitics.com)