Attacking midfielder Mkhitaryan, 24, had been linked with a move to Anfield after hitting 25 Ukrainian league goals for Shakhtar Donetsk last season.
But Dortmund swooped with a 24 million euro bid and he did not even speak to the Reds in the end, electing to be the high-profile replacement for Mario Goetze.
At his official presentation, Mkhitaryan said Dortmund’s recent success helped him make the decision.
“Liverpool have a great past,” he said. “But Borussia Dortmund has a great present.
“I made this decision with my heart.”
That Dortmund – who were last season’s runners up to Bayern Munich in both the Champions League and Bundesliga – can offer Champions League football, whereas Liverpool cannot, may have something to do with it.
Whatever his reasoning, he is happy to come to Germany, and not worried about the price tag, which starts at 24m euros but could rise to 27.5m euros.
“I have followed the Bundesliga in Ukraine and I know the standard is very high. I’m looking forward to it,” he added.
“I’m not worried about the transfer fee – I hope Dortmund don’t regret a cent of it.”
Mkhitaryan also shrugged off comparisons with Germany playmaker Goetze, who joined Bayern this summer.
“He’s a very good player but a very different type of player. You cannot compare us that easily.”