When Nagakatsu's adopted daughter, Nene, (later Kita no Mandokoro, Kodai-in) married Tokichiro KINOSHITA (later Hideyoshi TOYOTOMI), Nagamasa became the closest relative by marriage to Hideyoshi and, on Nobunaga's orders, became Hideyoshi's Yoriki (or adminisrative assistant).
長勝の養女となっていたねね（のちの北政所、高台院）が木下藤吉郎（後の豊臣秀吉）に嫁いだことから、長政は秀吉にもっとも近い姻戚として、信長の命で秀吉の与力となる。