The Star Trek: Voyager Companion describes B'Elanna as a young half-human half-Klingon in her twenties who is a member of the Maquis Rebellion.
The producers wanted to hire an actress who could portray B'Elanna's inner struggle between her human and Klingon halves. After Roxann Dawson read for the role, she became the first of the Voyager actors to be cast. Originally, Dawson's makeup differed from the final design; she explained that she had a much more pronounced Klingon forehead and nose and had to wear a set of Klingon teeth, which made her feel uncomfortable. She asked the producers and makeup artist Michael Westmore if they could perhaps make her more attractive and tone down the Klingon makeup. Eventually they came up with a design with which Roxann was happy, something she described as her "beauty monster makeup". Although B'Elanna's character was twenty-five years old when the series began, Dawson was actually thirty-six.
Dawson's initial reaction to the script of the first-season episode "Faces" was one of doubt; she felt that it occurred too early in the series and that she did not know the character well enough to play her as two separate people. However, she used the episode to learn more about her character, and it became one of her favorite episodes. When the episode aired, she called her parents to ask their opinions, and they replied, "You were good, but the girl that played that Klingon was really great!", which Dawson took as a compliment.
During the fourth season, Dawson became pregnant with her first child. The writers decided they did not want B'Elanna to be pregnant as well, so for the duration of Dawson's pregnancy, she was given an engineering lab coat, which was used to help cover her growing pregnancy. During the episode "The Killing Game", the Hirogen had taken over Voyager and forced the crew to participate in holodeck recreations of various combat situations, to which B'Elanna's holodeck character is portrayed as pregnant in World War II with a Nazi officer's child.
During the fifth season, Dawson had a meeting with the producers and writers to discuss her character. Roxann explained to them that she felt B'Elanna had an extreme dark side that hadn't been explored, and from that discussion the episode "Extreme Risk" was created. Dawson stated that after the episode aired she received fan mail praising the issues of depression and inner conflict raised in the episode, with which many people identified.
During the sixth season, Dawson got the chance to explore B'Elanna's Klingon heritage thanks to an episode originally conceived by Ronald D. Moore for Star Trek: Deep Space Nine. In the episode "Barge of the Dead", B'Elanna has a near-death experience and travels to Grethor, the Klingon Hell, where she meets her mother Miral. She discovers that because of the dishonor B'Elanna has caused her family, her mother would spend eternity in Grethor. The episode explores some aspects of B'Elanna's character, and also gives further insight into Klingon mythology. Dawson believed the episode had many layers to it, and she believed it was essentially a coming-of-age story for B'Elanna and her final acceptance of her Klingon heritage.
During the seventh season, a pregnancy storyline was written in for B'Elanna's character. Jessica Gaona played the character's young iteration in the episode "Lineage". At the end of the series, Dawson described B'Elanna's character arc as that of an unruly young woman who matures over the course of seven years.