Pope John I was not, foremost, a negotiator. He was a priest who upheld orthodoxy. He was killed for his orthodoxy.
Born about 470, son of a man named Constantius, John was a native of Tuscany. He took orders at a young age. We know that he was already a deacon by his signature on the Acts of the Roman Synod in 499 and 502. Thus, he was already in a position of some authority by the time he was 30. At the hotly debated election between Symmachus and Laurentian, when Laurentian became antipope, John had taken the side of Laurentian. Later, in 506, he realized his error and, in a legal document, he condemned Peter of Allinum, as well as Laurentian, and apologized profusely to Symmachus.
John was good friends with Boethius, the famous philosopher, theologian and educator, who dedicated three treatises to him as "Deacon John" in the time frame 512 - 520.
John was probably in his early 50s when he was elected pope after seven days of deliberation. He had been archdeacon under Pope Homisdas and, being fragile and sickly, was brave to accept the further responsibilities.
At the time of his election, Italy had been ruled for years by King Theodoric, king of Goths. An Arian, by belief, meaning he did not believe in the divinity of Christ, Theodoric was one who tolerated, or even favored, the Catholics who lived in his realm. However, two things happened right around the time of John's election. Theodoric, a suspicious type, discovered treasonous acts--correspondence between some members of the Roman Senate and Constantinople, his main enemy. Further, the new emperor of the Eastern empire, Justin, was a Catholic! The first Catholic to rule that empire in 50 years. Justin soon enacted an edict against heretics (read Arians) and ordered Arian clergy in the empire to surrender their churches into the hands of Catholic clergy.
Eastern Arians turned to the Arian emperor of the Western empire for help. At first Theodoric threatened war. Then he decided on negotiations with a delegation of five bishops and four senators, headed by Pope John. John could not get out of it. Religion and politics were impossibly intertwined.
Theodoric did not get everything he wanted. John convinced Justin to lessen his treatment of the Arians so that Theodoric would not retaliate on the good people of Italy. The Acacian schism, which began with Emperor Zeno's Henoticon 45 years before, ended. The Eastern patriarchs all manifested their communion with the Faith and with Rome. This was not upholding the Arians! This was supporting the orthodox Catholics! This was not at all in Theodoric's favor! The pope and the emperor closed negotiations with John celebrating Easter at Santa Sophia Church.
This all took a year and Theodoric was afraid that John and Justin were planning against him. Who knew how many others plotted against him! He ordered the execution of Boethius and his father-in-law, Senator Symmachus (not the same as the pope of the same name) on charges of treason.
John returned to Ravenna, Theodoric's capital, within weeks of Easter. But by now, Theodoric was crazed by suspicion. He had John arrested and imprisoned. A sickly man, overtired by journeying, John did not live long in prison.
On a more pastoral note, John was credited to repairs to various cemeteries in Rome. He also was the pope who ratified the Alexandrian computation of Easter. Now you know why it changes dates.