The couple welcomed their first child, Alena Rose, on Sunday.
Kevin, 26, first announced his wife was in labor early Sunday morning on Twitter. After the birth, which was officially revealed through Dreft detergent's account, Jonas tweeted, "I'm so in love with her."
The couple, who revealed they were expecting in July, married in 2009. Their E! reality series, Married to Jonas, which follows their lives as husband and wife, premiered in 2012.