The tomb is the central focus of the entire complex of the Taj Mahal. It is a large, white marble structure standing on a square plinth and consists of a symmetrical building with an iwan (an arch-shaped doorway) topped by a large dome and finial. Like most Mughal tombs, the basic elements are Persian in origin.

The base structure is a large multi-chambered cube with chamfered corners forming an unequal eight-sided structure that is approximately 55 metres (180 ft) on each of the four long sides. Each side of the iwan is framed with a huge pishtaq or vaulted archway with two similarly shaped arched balconies stacked on either side. This motif of stacked pishtaqs is replicated on the chamfered corner areas, making the design completely symmetrical on all sides of the building. Four minarets frame the tomb, one at each corner of the plinth facing the chamfered corners. The main chamber houses the false sarcophagi of Mumtaz Mahal and Shah Jahan; the actual graves are at a lower level.

The most spectacular feature is the marble dome that surmounts the tomb. The dome is nearly 35 metres (115 ft) high which is close in measurement to the length of the base, and accentuated by the cylindrical "drum" it sits on which is approximately 7 metres (23 ft) high. Because of its shape, the dome is often called an onion dome or amrud (guava dome). The top is decorated with a lotus design which also serves to accentuate its height. The shape of the dome is emphasised by four smaller domed chattris (kiosks) placed at its corners, which replicate the onion shape of the main dome. The dome is slightly asymmetrical. Their columned bases open through the roof of the tomb and provide light to the interior. Tall decorative spires (guldastas) extend from edges of base walls, and provide visual emphasis to the height of the dome. The lotus motif is repeated on both the chattris and guldastas. The dome and chattris are topped by a gilded finial which mixes traditional Persian and Hindustani decorative elements.

The main finial was originally made of gold but was replaced by a copy made of gilded bronze in the early 19th century. This feature provides a clear example of integration of traditional Persian and Hindu decorative elements.[16] The finial is topped by a moon, a typical Islamic motif whose horns point heavenward.

The minarets, which are each more than 40 metres (130 ft) tall, display the designer's penchant for symmetry. They were designed as working minarets—a traditional element of mosques, used by the muezzin to call the Islamic faithful to prayer. Each minaret is effectively divided into three equal parts by two working balconies that ring the tower. At the top of the tower is a final balcony surmounted by a chattri that mirrors the design of those on the tomb. The chattris all share the same decorative elements of a lotus design topped by a gilded finial. The minarets were constructed slightly outside of the plinth so that in the event of collapse, a typical occurrence with many tall constructions of the period, the material from the towers would tend to fall away from the tomb.

The interior chamber of the Taj Mahal reaches far beyond traditional decorative elements. The inlay work is not pietra dura, but a lapidary of precious and semiprecious gemstones. The inner chamber is an octagon with the design allowing for entry from each face, although only the door facing the garden to the south is used. The interior walls are about 25 metres (82 ft) high and are topped by a "false" interior dome decorated with a sun motif. Eight pishtaq arches define the space at ground level and, as with the exterior, each lower pishtaq is crowned by a second pishtaq about midway up the wall. The four central upper arches form balconies or viewing areas, and each balcony's exterior window has an intricate screen or jali cut from marble. In addition to the light from the balcony screens, light enters through roof openings covered by chattris at the corners. The octagonal marble screen or jali bordering the cenotaphs is made from eight marble panels carved through with intricate pierce work. The remaining surfaces are inlaid in delicate detail with semi-precious stones forming twining vines, fruits and flowers. Each chamber wall is highly decorated with dado bas-relief, intricate lapidary inlay and refined calligraphy panels which reflect, in miniature detail, the design elements seen throughout the exterior of the complex.