WASHINGTON—A top official with the National Security Council plans to tell House impeachment investigators that he was concerned by President Trump’s July phone call with Ukrainian President Volodymyr Zelensky, saying that the president’s request to have the Ukrainians investigate Joe Biden and his son may have been interpreted as a “partisan play.”

Alexander Vindman, an Iraq war veteran who currently oversees Ukraine policy at the NSC, will be the first official with firsthand knowledge of the phone call at the heart of the...