First, what is modalism?
Modalism maintains that there is one God who manifests Himself successively as Father, Son, and Holy Spirit but who is not contemporaneously all three. [Believer's Study Bible, electronic ed. (Nashville: Thomas Nelson, 1997), Glossary.]
The ESV Study Bible expands on this with this paragraph:
One of the most fundamental ways to misunderstand the Trinity is tritheism, which overemphasizes the distinction between the persons of the Trinity and ends up with three gods. This view neglects the oneness of the natures of Father, Son, and Holy Spirit. At the other end of the spectrum is the heresy of modalism (also known as Sabellianism, named after its earliest proponent, Sabellius, 3rd century), which loses the distinctions between the persons and claims that God is only one person. In this view, the appearance of the three persons is merely three modes of existence of the one God. For instance, God reveals himself as Father when he is creating and giving the law, as Son in redemption, and as Spirit in the church age. A contemporary version of modalism is found in the teaching of Oneness Pentecostalism. [Crossway Bibles, The ESV Study Bible (Wheaton, IL: Crossway Bibles, 2008), 2514-15.]
Sabellius, the man usually credited as the earliest proponent of the view was excommunicated by the Bishop of Alexandria in 260 or 261. The Sabellians appealed to Rome (the church in Rome played an early leading role, but there was as yet no papacy). In 262, the Bishop of Rome held a council and condemned Sabellius and his modalism along with tri-theism and subordinationism (an early variant of what would become Arianism).
False doctrines like modalism were condemned by the church in the third and fourth centuries. That settles the question, right?