Roger Sharratt, 52, of Bagots Oak in Staffordshire, had denied two counts of causing death by dangerous driving in May 2014.
Geoffrey Mills, 53, and Eleanor Joy Mills, 45, were killed in the collision, which happened near Harlow.
Sharratt, who was found guilty by a jury at Chelmsford Crown Court, will be sentenced on 2 June.
Police said Sharratt was driving a Man rigid lorry and drawbar goods vehicle northbound along the M11 when he went into the back of a black Jaguar XF car.
The Jaguar then collided with a silver Toyota Auris, pushing it under the back of a horsebox containing five horses from trainer Brian Meehan's stables.
The Toyota, carrying Geoffrey Mills and Eleanor Joy Mills, burst into flames and further collided with a white Vauxhall.
Police said Sharratt was driving at 55mph using cruise control and failed to react to the slowing traffic as he was likely to have been asleep.
Sharratt had only slept for three to four hours the night before the collision.
Det Insp Scott Egerton said: "Although this has been a complex case involving medical experts, Mr Sharratt drove dangerously.
"He was in charge of a heavy good vehicle and fell asleep.
"This case must serve as a warning to all drivers of the need to rest and take breaks when driving long distances.
"Mr Sharratt failed to do this and caused the most serious of crashes."
A lorry driver who fell asleep at the wheel has been found guilty of causing two deaths in a crash on the M11.