The 1916 publication in Annalen der Physik, 49, 769–822, also published separately in Leipzig, see e.g. Sauer, Albert Einstein's 1916 Review Article on General Relativity:
"The first comprehensive overview of the final version of the general theory of relativity was published by Einstein in 1916 after several expositions of preliminary versions and latest revisions of the theory in November 1915."
This was the paper the circumstances of whose submission and publication led to the Einstein and Hilbert priority dispute. It was not his first publication on general relativity, but it added the final piece, the field equations, see Janssen, Einstein’s First Systematic Exposition of General Relativity:
"Einstein’s first paper on a metric theory of gravity, co-authored with his mathematician friend Marcel Grossmann, was published as a separatum in early 1913 and was reprinted the following year in Zeitschrift für Mathematik und Physik (Einstein and Grossmann 1913, 1914a). Their second (and last) joint paper on the theory also appeared in this journal (Einstein and Grossmann 1914b). Most of the formalism of general relativity as we know it today was already in place in this Einstein-Grossmann theory. Still missing were the generally-covariant Einstein field equations."
And Einstein vaguely pondered modifications to Newtonian gravity to reconcile them with special relativity already back in 1907, in Über das Relativitätsprinzip und die aus demselben gezogenen Folgerungen, Jahrbuch der Radioaktivität und Elektronik 4, 411–462.