Reuters reported that Lesser had been interviewed for the chief executive role at WarnerMedia, AT&T’s media unit, but did not get the job. According to sources, Lesser "felt comfortable stepping down because Xandr is in a good position" and its forthcoming results are expected to reflect that.
Elsewhere in advertising, some have been sceptical of Xandr’s prospects, describing its progress as slow.
It is not confirmed whether a successor is lined up to replace Lesser. He reported to AT&T chief operating officer John Stankey, who is also chief executive of WarnerMedia.
Xandr was launched in 2018 when AT&T unveiled its joint advertising venture with AppNexus, which it had acquired earlier that year from WPP.
Lesser, who was former chief executive of AT&T Advertising & Analytics, was appointed to run the business, which claimed to bring together AT&T’s advertising and analytics operations under a single roof.
AT&T has spent $134bn on acquisitions of satellite-TV service DirecTV and Time Warner as it ups the stakes against competition from the likes of Netflix.