Jack Sargeant, 23, paid tribute to a "special community" as he became Labour's new Welsh Assembly member for Alyn and Deeside on Tuesday.
He called it a by-election "we shouldn't be fighting" in a "cold, wet, windy February", but used his victory speech to declare that now is not the time for questions about its cause.
Carl Sargeant, 49, was found dead in November after being suspended by Labour following unspecified allegations about his personal conduct. He is understood to have taken his own life.
Paying tribute to his father after increasing the party's vote share by more than 15%, Mr Sargeant thanked family and friends who "have supported me day in, day out, not just during this campaign but forever."
He said: "Above all, I want to say a big thank you to every person standing in this room tonight, everyone across Wales, across the UK and across the world as well who have stood by my family during the toughest time of our lives.
"This is a by-election here that we shouldn't be fighting in. None of the candidates on stage I'm sure, nor the people here supporting them, didn't expect to be going into a by-election certainly in February; a cold, wet, windy February.