The 30-year-old midfielder had admitted he was "sad" to leave the Toffees following his loan spell in the second half of the 2011-12 season, and said that David Moyes promised he would try to help him return if the opportunity arose.
During his year-long spell at Tottenham, Pienaar made only 18 appearances, scoring just one goal - but in six months at loan at Everton he scored four times in only 14 appearances.
"At the end of the season I was sad to say goodbye," Pienaar told Sky Sports.
"I spoke to the manager just before I left and that's when I made up my mind I wanted to come back to the club.
"I made it very clear to the manager here that if the opportunity came I really wanted to come back and he promised me he'd do whatever it took to make it happen. I'm glad he showed so much belief in me to bring me back."
The South Africa international said that his mind was made up before he returned to Spurs - and that the appointment of Andre Villas-Boas at the beginning of July changed nothing
"I followed my heart and told myself I'd made up my mind already before I went back to training," he said.
"We sat down, we talked and he [Villas-Boas] asked me how I felt.
"I told him: 'It was just clear before you came that I wanted to move, so nothing will change my mind - I will just be professional and work hard if nothing comes up'. So he understood my situation."