The 21-year-old becomes Bielsa's fourth signing of the summer.
He would go on to make four Championship appearances for Boro, and the Englishman is excited to start a new challenge under an attacking manager such as Bielsa.
"I have heard a little about him, speaking with Pep on his ideals and philosophies which was very interesting. There are some similarities," Harrison told Sky Sports News.
"It is great to be somewhere I can be close to Manchester and to work with Marcelo. I am really looking forward to working with him.
"Any young player would jump at the opportunity to work with the likes of Bielsa to look to improve themselves as much as possible. That is exactly what I am going to try and do.
"I will be given an opportunity to try and prove myself which is exactly what I need. [Guardiola] told me he is a great opportunity so to be hearing that is very encouraging."