The present brick cathedral was built mainly between about 1260 and 1340 as a three-aisled hall church in Gothic style, consecrated to Saints Peter and Paul during the 1330s. This original core, known as the Kärnkyrkan, was extended over the following two centuries with side chapels, burial chapels, a sacristy and a polygonal high choir with an ambulatory, completed and consecrated in 1462 under Bishop Sigge Ulfsson Sparre. The 75-metre tower, rebuilt several times, has carried its distinctive Baroque cupola since the mid-1700s.
Bishop Kort Rogge, who held the see from 1479 to 1501, left a particularly strong mark: after a fire in 1473 he raised the tower and unified the roofline, and he commissioned two Flemish altarpieces from workshops in Brussels. The larger, made in 1490 and known as the Roggeskåpet, dominates the high altar and is considered one of Sweden's largest and most important medieval altarpieces, alongside a smaller passion altarpiece and a Marian altarpiece attributed to the workshop of Jan Borman, dated around 1507–1508. Late-medieval wall and vault paintings, attributed to an anonymous decorative painter known as the Strängnäsmästaren, cover much of the choir vaulting with rich foliage ornament.```
Among the cathedral's furnishings is a white-and-gold Gustavian pulpit made around 1789 by court sculptor Pehr Ljung, a bronze font from the 1300s, and a limestone font of Gotland workmanship from around 1300. A wooden figure of Saint Eric, attributed to the Lübeck master Bernt Notke around 1490, is now kept in the Martyrs' Chapel, created in 1999 within the former Sack-Gyllenborg burial chapel to commemorate twentieth-century Christian martyrs.
The cathedral is also a significant burial place, containing the tomb of King Karl IX and Kristina of Holstein-Gottorp, the monument to Sten Sture the Elder, regent of Sweden, and a small limestone effigy of Princess Isabella, said to be among Sweden's earliest surviving child portraits. The Gyllenhielm burial chapel holds an elaborate marble and sandstone monument to admiral Carl Carlsson Gyllenhielm, attributed to a German or Netherlandish sculptor of the earlier seventeenth century.
In 2018 the cathedral's royal funerary regalia — crowns, orbs and sceptres made for Karl IX and Kristina — were stolen; they were recovered in poor condition the following year and, after restoration, a new display reportedly opened in 2020, though current viewing arrangements are not covered here. The cathedral also houses one of Sweden's oldest working libraries, tracing its origins to a 1316 book bequest and later enriched by Bishop Rogge and by war booty acquired in the 1600s.
A major restoration between 1907 and 1910, led by Fredrik Lilljekvist with Sigurd Curman advising, added Art Nouveau furnishings while pioneering conservation principles that respected earlier layers of the building — work often credited with helping the cathedral retain more of its medieval character than any other in Sweden.