He first appeared at the Legion's prospective member night in "L.O.D.R.S.V.P." when Harley Quinn and KGBeast were nominated against each other to join. He was seen mingling with Calendar Man at the beginning of the party and was present when Aquaman crashed the party. After she defeated Aquaman, Solomon Grundy witnessed as Harley Quinn was announced as the newest member of the Legion of Doom.
Solomon Grundy was in the audience as she was officially welcomed in the following episode. He also attended the Legion's weekly board meeting and voted to approve Joker's idea of building a tower until Harley started questioning his plans.
In "Something Borrowed, Something Green", he was a guest at Poison Ivy and Kite Man's wedding and was seen mingling with Bane before the ceremony. After the ceremony was hijacked by the GCPD, Solomon Grundy participated in the chaos that ensued and fought back against the officers.