The former Portsmouth striker, 26, was also convicted of failing to declare who was driving his Land Rover at the time of the offences.
Chelmsford Magistrates' Court heard that the star was caught breaking a 50mph speed limit on the M11 at Chigwell, Essex, in April and June last year.
Defoe was caught driving at 65mph just after midnight on April 16 last year and then at 81mph at about 9pm on June 6 last year.
The court heard a temporary speed limit of 50mph had been in place at the time.
Delivering his verdicts, Mark Jabbitt, the Deputy District Judge said: "In effect this was a technical assault on the evidence which I find has no merit.
"The evidence was not challenged in any real sense and as a result I find that he [Defoe] was the driver on each occasion.
"If Mr Defoe had wanted to assert anything he could have come to court today - that would have been an issue of substance."
Defoe, who already has six points on his licence - three for speeding and three for using a mobile phone while driving - is set to have a further 18 points slapped on as a result of today's convictions, meaning an automatic ban under the totting up procedure.