Szass Tam had a deal with Larloch, searching for ancient magic items and artifacts for him in exchange for some of Larloch's.

Even though Szass Tam had dozens of attendants over the years, one - Charmaine - served the lich for decades (by 1364 DR) in exchange for food and a promise of immortality later granted. Tam appreciated a loyal servant and anticipated making her his loyal servant forever.

Szass Tam was born in 1104 DR. In 1157 DR he led a group of Red Wizards to slay Nyressa Flass, the Zulkir of necromancy. Afterward, Tam was named the successor to the Zulkir of necromancy.

Before becoming a lich, one of his bitter rivals was a fellow Red Wizard from the school of evocation whom Szass Tam faced in a spell-slinging duel. The other Red Wizard was prepared to face Tam's necromancy spells and was caught off-guard when the future lich flung twelve fireballs into his face using a necklace of fireballs. This prompted Tam's opponent to waste most of his spells in deflecting and defending against the infernal onslaught, while Szass Tam had his entire repertoire of memorized spells at his disposal. Needless to say, the future undead emerged victorious.

In 1159 DR Szass Tam became a lich after an abortive invasion of Rashemen.

At some point, Tam inherited his favorite polished, enchanted, several-hundred-years-old crystal ball that belonged to his mentor, after the lich killed him. Tam increased his arcane powers after wresting all sorts of arcane devices, elixirs, and books from his dead teacher.

In 1201 DR Szass Tam slew the Zulkir of illusion, Nymor Thrul after a failed invasion of Aglarond. Tam later slew the Harper King, but was defeated himself by Elminster Aumar in 1222 DR. In 1359 DR Tam allied Thay with the Tuigan horde. Working through Harper agents, Tam defeated Maligor Zulkir of Alteration. In 1367 DR Tam released the demon lord Eltab that destroyed much of Eltabbar. Tam unleashed a horde of undead to attack Aglarond, but failed to breach the Watchwall. In 1373 DR he aided Thazienne Uskevren to release Eltab.

In 1375 DR, Tam caused the murders of the Zulkirs Druxus Rhym and Aznar Thrul and betrayed a Thayan army, under the command of tharchions Azhir Kren and Homen Odesseiron, to the Rashemi to create a climate of fear within the Thayan population. He hindered the proper investigation of the murders and solved these issues by himself. He thus tried to convince the nobles, legions and common people that he was the only one who could deal with these problems, in order to get himself elected supreme ruler of Thay. When Dmitra Flass rallied the Zulkirs originally loyal to him to stand against his aspirations, Tam decided to achieve rulership by force and declared war to all opposing Zulkirs. When Dmitra's council achieved a great victory against his undead army at the Keep of Thazar, Tam called upon the united armies of Gauros and Surthay to march south toward the great city of Bezantur.

By 1377 DR Szass Tam had established his seat of power at Thaymount by evicting his enemies from their estates on the plateau. Some of the Zulkirs changed sides a couple times during the war and ended up as Tam's allies. One of them was the diviner Yaphyll. However, after realizing that Thay under the lich's reign would be comprised of undead, she decided to switch sides again in favor of the council of Zulkirs. As a result, Tam took her prisoner in 1385 DR, binding her with the Death moon orb and Thakorsil's Seat, powerful artifacts of domination. He forced Yaphyll to perform the most powerful divination known to her order, no matter the consequences to her own well-being, and to tell him how to arrange for a decisive victory over the other Zulkirs. She performed the task and told Tam to lay a trap at the Keep of Sorrows. Then she left him with another vision:

“The white queen is troubled but can't say why. The black queen hates the white and gives the assassin a black coat. The assassin steals upon the white queen. She can't see him gliding through the shadows. The sword screams. The white queen falls. Her city falls. Stones fall in the cavern to crush the soothsayer. The tree burns and thrashes in agony. Branches break. Branches twist and grow together...”
— Yaphyll's vision

At the end of the vision Yaphyll was surrounded by a blue flame and broke free of Szass Tam's power. The lich killed her with his poisonous touch trying to regain control over the diviner. Later it became apparent that Yaphyll saw what became known as the Spellplague, the blue flames being a result of the event. As Yaphyll predicted, the fight at the Keep of Sorrows turned into Tam's favor. With the help of the Death Moon Orb, he tried to coerce his former ally Dmitra Flass into fighting for his side. But then the Spellplague hit. The Death Moon Orb exploded in Tam's hand, freeing Dmitra of its power. Tam was hit by a wave of azure fire, a result of the Spellplague, rendering his magic close to useless and burning the flesh from his face and hands. The lich fled from the scene with the help of Xingax.

By revealing to Malark Springhill why he killed Druxus Rhym, the lich convinced the spymaster to switch sides and work for him and his greater cause henceforth.

In order to learn more about the ways of magic in the time of the Spellplague, Tam summoned Bane, sacrificing the tharchion Pyras Autorian in the ritual. Bane made a bargain with the lich: he would reveal to Tam his knowledge about the chaotic magic, grant the lich the ability to raise more dead for his cause, and augment the lich's powers. Tam, in turn, agreed to surrender his soul after 1000 years had passed when his quest of conquering Thay was completed.[38] Tam knew that the mystical strength lent to him by Bane would gradually fade so he choose to exploit it immediately.

When it came to another fight at the Keep of Sorrows, Szass Tam summoned a dream vestige to turn the tide in his favor. He succeeded in beating the legions of the Zulkirs, chasing them all the way to Bezantur. His undead legions and loyal priests of Bane further forced the Zulkirs to leave the town aboard vessels. Tam summoned the bodies of drowned men and undead aquatic beasts for a final and lethal victory over the Zulkirs. Accompanied by a fleet of warships made from darkness, he followed the fleeing Zulkirs, entangling them in a marine war. His enemies and Nevron's conjured denizens of the infernal oceans proved quite adept at sea fight, beating back his undead minions. Tam conjured the dream vestige again, finally exhausting his magical powers bestowed by Bane. When Bareris defeated the dream vestige and the Zulkir's forces beat Szass Tam's minions, the lich and Malark withdrew to the Thaymount, the lich being content with his conquered lands.

Tam didn't bother chasing the remaining Zulkirs any more, leaving Alaor and the Wizard's Reach to them, not fearing any retribution by the depleted Zulkir's forces. He revealed to Malark that he found a book once in possession of Fastrin the Delver.