Methylates (mono- and asymmetric dimethylation) the guanidino nitrogens of arginyl residues in several proteins involved in DNA packaging, transcription regulation, pre-mRNA splicing, and mRNA stability. Recruited to promoters upon gene activation together with histone acetyltransferases from EP300/P300 and p160 families, methylates histone H3 at 'Arg-17' (H3R17me), forming mainly asymmetric dimethylarginine (H3R17me2a), leading to activates transcription via chromatin remodeling. During nuclear hormone receptor activation and TCF7L2/TCF4 activation, acts synergically with EP300/P300 and either one of the p160 histone acetyltransferases NCOA1/SRC1, NCOA2/GRIP1 and NCOA3/ACTR or CTNNB1/beta-catenin to activate transcription. During myogenic transcriptional activation, acts together with NCOA3/ACTR as a coactivator for MEF2C. During monocyte inflammatory stimulation, acts together with EP300/P300 as a coactivator for NF-kappa-B. Acts as coactivator for PPARG, promotes adipocyte differentiation and the accumulation of brown fat tissue. Plays a role in the regulation of pre-mRNA alternative splicing by methylation of splicing factors. Also seems to be involved in p53/TP53 transcriptional activation. Methylates EP300/P300, both at 'Arg-2142', which may loosen its interaction with NCOA2/GRIP1, and at 'Arg-580' and 'Arg-604' in the KIX domain, which impairs its interaction with CREB and inhibits CREB-dependent transcriptional activation. Also methylates arginine residues in RNA-binding proteins PABPC1, ELAVL1 and ELAV4, which may affect their mRNA-stabilizing properties and the half-life of their target mRNAs. Acts as a transcriptional coactivator of ACACA/acetyl-CoA carboxylase by enriching H3R17 methylation at its promoter, thereby positively regulating fatty acid synthesis (PubMed:30366907). L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Methylation of H3R17 (H3R17me) by CARM1 is stimulated by preacetylation of H3 'Lys-18' (H3K18ac) H3 'Lys-23' (H3K23ac) by EP300 and blocked by citrullination of H3 'Arg-17' (H3R17ci) by PADI4. Homodimer. Interacts with NR1H4. Interacts with SNRPC (By similarity). Interacts with the C-terminus of NCOA2/GRIP1, NCO3/ACTR and NCOA1/SRC1. Part of a complex consisting of CARM1, EP300/P300 and NCOA2/GRIP1. Interacts with FLII, TP53, myogenic factor MEF2, EP300/P300, TRIM24, CREBBP and CTNNB1. Interacts with RELA. Identified in a complex containing CARM1, TRIM24 and NCOA2/GRIP1. Interacts with NCOA3/SRC3. Interacts with SKP2 (PubMed:30366907). Interacts (via PH domain-like fold) with C9orf72 (PubMed:30366907). Mainly nuclear during the G1, S and G2 phases of the cell cycle (By similarity). Cytoplasmic during mitosis, after breakup of the nuclear membrane (By similarity). Ubiquitously expressed. Within the brain, present in proliferating cells from lateral ventricular zone and dentate gyrus (at protein level). At 9 dpc, expression is prominent in the neural tube and somites. Phosphorylation at Ser-217 is strongly increased during mitosis, and decreases rapidly to a very low, basal level after entry into the G1 phase of the cell cycle (By similarity). Phosphorylation at Ser-217 interferes with S-adenosyl-L-methionine binding and strongly reduces methyltransferase activity. Phosphorylation at Ser-217 may promote cytosolic location. Auto-methylated on Arg-551. Methylation enhances transcription coactivator activity. Methylation is required for its role in the regulation of pre-mRNA alternative splicing. Neonatal lethality. The lungs of neonates do not inflate and they do not breathe. The same neonate lethality is observed with mutants that produce CARM1 protein without enzyme activity. Embryos are distinctly smaller at 18.5 dpc. They show reduced lipid accumulation in brown adipose tissue and reduced amounts of brown adipose tissue. Thymocyte differentiation is blocked at an early stage. Mutants display complete loss of protein methylation of the CARM1 substrates PABPC1 and EP300/P300. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family.