Methylates (mono- and asymmetric dimethylation) the guanidino nitrogens of arginyl residues in several proteins involved in DNA packaging, transcription regulation, and mRNA stability. Recruited to promoters upon gene activation, methylates histone H3 and activates transcription via chromatin remodeling. L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family.