Lessing was born in Kamenz, a little town in Saxony. His father was a clergyman and the author of theological writings. After attending Latin School in Kamenz (from 1737 onwards) and the Fürstenschule St. Afra in Meissen (from 1741 onwards) he studied theology and medicine in Leipzig (1746 – 1748).

From 1748 to 1760 he lived in Leipzig and Berlin and worked as reviewer and editor for, amongst others, the Vossische Zeitung. In 1752 he took his Master's degree in Wittenberg. From 1760 to 1765 he worked in Breslau (now Wrocław) as secretary to General Tauentzien. In 1765 he returned to Berlin, only to leave again in 1767 to work for three years as a dramaturg and adviser at the German National Theatre in Hamburg. There he met Eva König, his future wife.

In 1770 Lessing became a librarian at the Herzog-August-Bibliothek in Wolfenbüttel. His tenure there was interrupted by many travels. For example, in 1775 he journeyed to Italy accompanied by Prince Leopold. In 1771 Lessing was initiated into Freemasonry in the lodge "Zu den drei Rosen" in Hamburg.

In 1776 he married Eva König, who was then a widow, in Jork (near Hamburg). She died in 1778 after giving birth to a short lived son. On 15 February 1781, Lessing, at 52, died during a visit to the wine dealer Angott in Braunschweig.

Lessing was also famous for his friendship with Jewish - German philosopher Moses Mendelssohn. In his celebrated biography of Mendelssohn's famous grandson, Felix, Larry Todd describes their friendship as one of the most "illuminating metaphors [for] the clarion call of the Enlightenment for religious tolerance".

Lessing was a poet, philosopher and critic. His theoretical and critical writings are remarkable for their often witty and ironic style and their unerring polemics. Hereby the stylistic device of dialogue met with his intention of looking at a thought from different angles and searching for elements of truth even in the arguments made by his opponents. For him this truth was never solid or something which could be owned by someone but always a process of approaching.

Early in his life, Lessing showed interest in the theatre. In his theoretical and critical writings on the subject — as in his own plays — he tried to contribute to the development of a new bourgeois theatre in Germany. With this he especially turned against the then predominant literary theory of Gottsched and his followers. He particularly criticized the simple imitation of the French example and pleaded for a recollection of the classic theorems of Aristotle and for a serious reception of Shakespeare's works. He worked with many theatre groups (e.g. the one of the Neuberin). In Hamburg he tried with others to set up the German National Theatre. Today his own works appear as prototypes of the later developed bourgeois German drama. Scholars generally see Miß Sara Sampson and Emilia Galotti as the first bourgeois tragedies, Minna von Barnhelm (Minna of Barnhelm) as the model for many classic German comedies, Nathan the Wise (Nathan der Weise) as the first German drama of ideas ("Ideendrama"). His theoretical writings Laocoon and Hamburg Dramaturgy (Hamburgische Dramaturgie) set the standards for the discussion of aesthetic and literary theoretical principles.

In his religious and philosophical writings he defended the faithful Christian's right for freedom of thought. He argued against the belief in revelation and the holding on to a literal interpretation of the Bible by the predominant orthodox doctrine through a problem later to be called Lessing's Ditch. Lessing outlined the concept of the religious "Proof of Power": How can miracles continue to be used as a base for Christianity when we have no proof of miracles? Historical truths which are in doubt cannot be used to prove metaphysical truths (such as God's existence). As Lessing says it: "That, then, is the ugly great ditch which I cannot cross, however often and however earnestly I have tried to make that leap."

As a child of the Enlightenment he trusted in a "Christianity of Reason", which oriented itself by the spirit of religion. He believed that human reason (initiated by criticism and dissent) would develop, even without help by a divine revelation. In addition, he spoke up for tolerance of the other world religions in many arguments with representatives of the predominant schools of thought (e.g. within the "Anti-Goeze"). He also worked this position into his dramatic work (in Nathan der Weise) when he was forbidden to publish further theoretical writings. In his writing The Education of Humankind (Die Erziehung des Menschengeschlechts) he extensively and coherently lays out his position.

The idea of freedom (for the theatre against the dominance of its French model; for religion from the church's dogma) is his central theme throughout his life. Therefore he also stood up for the liberation of the upcoming bourgeoisie from the nobility making up their minds for them.

In his own literary existence he also constantly strove for independence. But his ideal of a possible life as a free author was hard to keep up against the economic constraints he faced. His project of authors self-publishing their works, which he tried to accomplish in Hamburg with C.J. Bode, failed.

Lessing is important as a literary critic for his work Laocoon: An Essay on the Limits of Painting and Poetry. In this work, he argues against the tendency to take Horace's ut pictura poesis (as painting, so poetry) as prescriptive for literature. In other words, he objected to trying to write poetry using the same devices as one would in painting. Instead, poetry and painting each has its character (the former is extended in time; the latter is extended in space). This is related to Lessing's turn from French classicism to Aristotelian mimesis.