After the death of Ivan Alexander in early 1371, Ivan Shishman inherited the central portion of Bulgaria with the capital Tarnovo. Ivan Sratsimir of Vidin and Dobrotitsa/Dobrotici of Dobrudzha were completely independent. Although in 1371 Wallachia still recognized the suzerainty of Ivan Alexander as seen in a request concerning commercial, in 1386, during an obscure war in which Ivan Shishman defeated and killed Dan I of Wallachia, it was probably already independent. That year, Ivan Shishman had attacked Ivanko, the new despot of Dobrudzha, who was the nephew of Dan I, but although he killed Ivanko's ally, he didn't manage to bring Dobdruja under his influence.
The reign of Ivan Shishman is inextricably connected with the fall of Bulgaria under Ottoman domination. Shortly after Ivan Shishman came to the throne, the united forces of the Serbian nobles led by King Vukašin Mrnjavčević were defeated by the Ottoman Turks in the battle of Černomen on September 26, 1371. The Ottomans advanced on Bulgaria, and Ivan Shishman was forced to recognize Ottoman overlordship and to send his sister Thamar (Kera Tamara) as a spouse for Sultan Murat I by 1373.
In spite of this capitulation, the Ottomans continued their conquest of Bulgaria, with the fall of Ihtiman in 1378, Sofia in 1383 and Niš in 1385. Encouraged by the Serbian and Bosnian victory over the Ottomans at the Battle of Pločnik in 1387, Ivan Shishman refused to support Murat I or to recognize his suzerainty. The Ottoman reprisal was swift, and the enemy overran the Bulgarian defenses, besieging Ivan Shishman in Nikopol on the Danube in 1388. Ivan Shishman had no choice but to submit, and was allowed to keep most of his realm, but was required to surrender Drastar (Silistra) to the Ottoman Sultan. Ivan Shishman tried to go back on his promises, and found himself besieged in Nikopol again, surrendered Drastar, and allowed the introduction of Ottoman garrisons in other important fortresses.
In spite of the murder of Sultan Murat I before the Battle of Kosovo in 1389, the Ottomans crushed the Christian coalition, and could turn their attention more closely to Ivan Shishman. In 1393 the new Sultan Bayezit I invaded Bulgaria unexpectedly and besieged the capital Tarnovo. The capital was defended under the supervision of the Bulgarian Patriarch Evtimiy, while Ivan Shishman had taken refuge in Nikopol once more. After a siege of three months, Tarnovo fell by treason on July 17, 1393, a point sometimes taken as the end of the Second Bulgarian Empire, although both Ivan Shishman and Ivan Sratsimir survived.
Ivan Shishman continued to rule in Nikopol as an Ottoman vassal, and perhaps counted on the imminent anti-Ottoman crusade prepared by the Hungarian king Sigismund of Luxemburg. Returning from a failed campaign against Mircea I of Wallachia, Sultan Bayezit I had Ivan Shishman beheaded at Nikopol on June 3, 1395. The remainder of Ivan Shishman's territory was annexed by the Ottoman Empire, while Bulgarian emperors continued to rule at Vidin until 1422.
Tradition presents Ivan Shishman as the last emperor of Bulgaria, commemorated in legends and folk songs placing his heroic exploits or death in virtually every corner of the country. Ivan Shishman was in fact survived by his half-brother Ivan Sratsimir in Vidin and the latter's son Constantine II. Although it cannot be denied that Ivan Shishman was a far more energetic ruler than Ivan Sratsimir, his heroism finds little expression in the sources. In them he appears as a vacillating politician whose inopportune choices speedily guided him to his violent end and the subjugation of the country by the enemy. This judgment has the natural benefit of hindsight, and the increasingly difficult situation of Bulgaria during this period was hardly entirely Ivan Shishman's doing.
Ivan Shishman was married first to a Bulgarian named Kera Marija, who died in the early 1380s. He married as his second wife Dragana, a daughter of prince Lazar I of Serbia. From either of his marriages, Ivan Shishman had several children, including: