The Japanese star had not won a tournament since Memphis in 2016 and was hampered by a wrist injury the following year which forced a break from the 2018 tour.
He was runner-up in Brisbane in 2017 but went one better this year in a superb final.
Nishikori dominated his Russian rival throughout, despite a slight hiccup when one poor service game cost him the second set.
The second seed started slowly and went down 0-3 to the Russian.
But he recovered to break back and then seized the advantage at 3-3 when he broke Medvedev again, taking the first set in 42 minutes.
Nishikori was all over the Russian in the second set, his powerful and well-directed groundstrokes forcing Medvedev into errors.
Medvedev held on against Nishikori’s multiple chances to break at 2-2 and 3-3 and took advantage of his opponent’s poor service game to break ahead.
“I felt like in the second set I was a little bit, like waiting too much and I couldn’t convert all the chances I had,” the Russian said.
“And he did really well the last game, I mean the 4-3 game. He took the risk and he did well and credit to him for second set.
“I had so many chances and I thought I could win in two sets.”
Any thought Medvedev would take the momentum into the decider proved wrong as Nishikori stormed to a 5-1 lead, eventually wrapping up the final in just over two hours.
“I realised I had to do something to win this match and I think I made a change really well,” he said.
“I think I returned well — that was the biggest key, I think. I was able to return very deep and I think I put him under pressure.”
Nishikori said he was pleased with his form heading into the Australian Open, a tournament at which he has never progressed further than the quarter-finals.
“The main goal is to do well in Australian Open, but I’m really happy that I’ve been playing really well this week,” he said.
“Even if I lost today, I think I was very confident, and some of the matches I played some of the best (players).
“So, I’m happy to go in Melbourne, and I feel like it’s one of my favourite tournaments there.
“I feel like I have much support and feel almost home there so I hope I can do well better than quarter-final.”
(AFP)
