The measure of real matrices that are not diagonalizable over $\mathbb{C}$ equals to 0, see for example On the computation of Jordan canonical form, so the probability for a random matrix with a continuous probability distribution to be non-diagonalizable is 0.

The measure of real matrices that are not diagonalizable over $\mathbb{C}$ equals to 0, see for example On the computation of Jordan canonical form, so the probability for a random matrix with a continuous probability distribution to be non-diagonalizable vanishes. To put it differently, the set of real matrices without multiple eigenvalues is dense, and a matrix without multiple eigenvalues is definitely diagonalizable.

I misread "singular" for "diagonalizable".

The measure of real matrices that are not diagonalizable over $\mathbb{C}$ equals to 0, see for example On the computation of Jordan canonical form, so the probability for a random matrix with a continuous probability distribution to be non-diagonalizable is 0.