Aspinall never found himself behind in front of a packed house in Gottingen, Germany as he earned his first title since the World Matchplay in 2023.
'The Asp' defeated Ritchie Edhouse, Jermaine Wattimena, world number one Luke Humphries and Gary Anderson en route to the final, where he impressed.
Aspinall averaged over 98 and threw five 180s in an encounter where he raced 4-1 up before Joyce – playing in his first European Tour final – showed a response.
The lead was cut to 5-4 but Aspinall proved too strong for Joyce as he pulled out the victory and £30,000 in prize money.
"It felt like it was written in the stars," Aspinall said afterwards. "Ryan is a great guy and a top player, and it was great to share the stage with him in the final.
"This is what I needed. This will help me believe in myself and it shows I'm still good enough to compete against the top boys.
"Because of the situation I've been in over the last few years with the injuries and the dartitis, this is probably my proudest moment.
"The crowd were unbelievable. The support I got was amazing. This honestly means so much to me."
Joyce produced some impressive displays to reach the final, which included a whitewash win over Joe Cullen on Friday before seeing off Dimitri Van den Bergh, Rob Cross and Cameron Menzies.
The 39-year-old then stunned Michael van Gerwen 7-5 in the semi-finals to book his place in the showpiece.