"As a person who has always worked in the field of peace and negotiation, I truly consider him not just a champion of fight against terrorists, but also a hero in peace-making efforts," Zarif said in a televised interview on Sunday night.
The Iranian top diplomat said he always consulted with General Soleimani, and his advice was always "useful" to him.
"In the time when I was Iran's ambassador and permanent (UN) representative in the US, and during the negotiations I had been ordered by the Supreme Leader to hold, I used to come back to Tehran to consult with Hajj Qassem, and then leave the country to hold negotiations," Zarif said.
"Hajj Qassem's consultations were always useful to me, and I really didn't take any advice from other people. Once I asked the Supreme Leader to allow Hajj Qassem to personally participate in the session, and I was sure the talks would have been much more successful (with him in attendance)," he added.
Zarif further praised Soleimani's personal characteristics, describing him as a person who cared about people's lives, reputation, and end of conflicts.
"Any peace plan I pursued had definitely been devised by Hajj Qassem; he both encouraged us and helped us with the follow-ups," he added.
Zarif then highlighted the significant role played by General Soleimani in the 2001 Bonn Conference, which resulted in an agreement on the re-creation of the State of Afghanistan following the US invasion of the country.
"Hajj Qassem played a more important role in Tehran by holding talks with all jihadi groups of Afghanistan, to convince them to accept an equation which could shape a new future for Afghanistan in the years to come," he noted.
Zarif made the comments on the first anniversary of the assassination of General Soleimani, along with his comrades, in a US drone strike near the Baghdad International Airport.
In his Sunday remarks, the Iranian top diplomat slammed US President Donald Trump for assassinating Soleimani in such a "cowardly" way.
"Hajj Qassem used to tell me he was waiting for a bullet, and he thought he'd be shot in the battlefield. He would never think the Americans may hit a car in the mid-night in such a way. It was an easy job to hit that car… It really shows Trump's misery and cowardice," Zarif said.
"The Americans were terrified of Hajj Qassem and considered him a genius in the battlefront. He was a genius who had defeated them in Syria and Yemen," he added.
General Soleimani, who commanded the Quds Force of Iran's Islamic Revolution Guards Corps (IRGC), was admired as the Middle East's most influential and charismatic counterterrorism leader. He played a key role in helping Iraq and Syria defeat foreign-backed terrorists, chiefly Daesh, in late 2017.