The Renaissance artist is best known for great works such as the statue of David and the Sistine Chapel ceiling but he also left behind around 600 cartoons and drawings.
The scraps of writing on about a third of the drawings include lines of poetry, memos to his assistants, explanatory notes to some of his greatest works and "achingly personal expressions of ambition and despair surely meant for nobody's eyes but his own", according to Leonard Barkan, a professor of comparative literature at Princeton University.
In the margin of one drawing he carefully documented the money he had spent on chickens, oxen and his father's funeral.
Next to a drawing of a Madonna and child he wrote a parody of a love poem that began: "You have a face sweeter than boiled grape juice, and a snail seems to have passed over it."
Prof Barkan spent five years studying Michelangelo's written words and has produced a book, <i>Michelangelo: A Life on Paper</i>, with 200 reproductions of the artist's private papers.
On one sheet, he drew a large hand and two human figures, alongside expressions of longing, sadness and regret, including "Death is the end of a dark prison" and "Desire engenders desire and then leaves pain".
Another sheet features a playful drawing of a cherub next to lines from Petrarch in Latin.
Michelangelo's extraordinary achievements in sculpture and painting sometimes obscure the fact that he was also a poet, writing around 300 poems in his lifetime.
One poem, about the pain he feels for a lover, peters out with the word "dear", as if he could no longer bear to write down his feelings.
To underline the sentiment, he then turned the sheet 90 degrees and drew a sketch of his own hand, with the index finger pointing at "dear".
The juxtaposition of images and words provide an intimate insight into the artist's inner most thoughts, fears and desires, Prof Barkan said.