Route 63 is a secondary state highway in the U.S. state of Connecticut, from New Haven up to Canaan, running for 52.57 miles (84.60 km). It connects the Greater New Haven area to Northwestern Connecticut via the western suburbs of Waterbury.

Route 63 follows a mostly northwest-southeast path its entire route, and is mostly a 2 lane road with some 4 lane sections. It begins at the corner of Whalley Avenue and Fitch Street in New Haven where Route 10 turns onto Fitch Street. Heading northwest on Whalley Avenue, it almost immediately passes the eastern end of Route 243 and the northern end of Route 122. About 0.6 miles later, it leaves Whalley Avenue for Amity Road at the southern end of Route 69. It then passes under the Wilbur Cross Parkway (Route 15), offering southbound access only. After crossing into Woodbridge, the road becomes less suburban in nature. In Woodbridge, it intersects the eastern end of Route 114, and the southern/eastern end of Route 67. It then crosses into Bethany, where it has a brief (0.1 mile) concurrency with Route 42. It then enters Naugatuck, where the road takes on a more suburban character. It then meets the Route 8 expressway at Exit 26 before crossing the Naugatuck River into the downtown area. It then passes by the western end of Route 68 before becoming more rural again. After clipping the southwest corner of Waterbury, it enters Middlebury. After meeting the northern end of Route 188, it intersects I-84 at Exit 17, with access to/from the west. Access to/from I-84 east is provided by Route 64 at the next intersection. Route 63 then enters Litchfield County and the town of Watertown. Here it is a major retail strip in the southern part of town. It meets the northern end of Route 73 before crossing US 6 in the center of town. It then becomes a minor arterial road north of town, and passes by the eastern end of Route 132 before entering Morris. In Morris, it has junctions with Route 109 and the northern end of Route 61. It then enters Litchfield, where it meets US 202 at the Litchfield Green. Leaving Litchfield, Route 63 becomes a minor rural road as it passes into Goshen. It meets Route 4 at a traffic circle in the center of town. North of there, it passes into Cornwall, where it meets the north end of Route 43, then into the town of Canaan. It has one junction with the southern end of Route 126, which leads to Falls Village. Route 63 ends approximately 1.5 miles later at US 7.

A 3.4-mile (5.5 km) section of the road in Litchfield is a designated state scenic road.

Route 63 was designated in 1932 and originally connected Morris to Woodbridge using the alignment of the Straits Turnpike, an early 19th-century toll road connecting New Haven to Litchfield. Route 63 is still locally called the Straits Turnpike in Middlebury and Watertown. In the mid-1940s, Route 61 between Morris and Cornwall was reassigned to an extended Route 63. Another extension happened on September 11, 1951 when Route 63 took over part of Route 43 from Cornwall to Canaan where it ends today. In 1954, Route 63 was extended south to US 1 via an overlap with Route 10.

County	Location	mi	km	Destinations	Notes
New Haven	New Haven	0.00	0.00	Route 10 (Fitch Street / Whalley Avenue) – Hamden, Westville	Southern terminus
		0.12	0.19	Route 243 west – Ansonia	Eastern terminus of Route 243
		0.71	1.14	Route 122 south – Allingtown	Northern terminus of Route 122
		1.29	2.08	Route 69 north – Bethany, Prospect, Waterbury	Southern terminus of Route 69
		1.51	2.43	Route 15 south (Wilbur Cross Parkway) – New York City	Exit 59 on Route 15 / Wilbur Cross Parkway
	Woodbridge	1.75	2.82	Lucy Street (SR 749 east)
		2.85	4.59	Route 114 west – Orange	Eastern terminus of Route 114
		4.69	7.55	Route 67 west – Seymour	Eastern terminus of Route 67
	Bethany	9.75	15.69	To Route 42 west – Beacon Falls	Access via SR 703
		10.04	16.16	Route 42 west – Beacon Falls	Southern end of Route 42 concurrency
		10.14	16.32	Route 42 east – Cheshire	Northern end of Route 42 concurrency
	Naugatuck	14.40	23.17	Route 8 / South Main Street (SR 709 north) – Bridgeport, Waterbury	Exit 25A on Route 8
		15.80	25.43	Route 68 east – Prospect, Waterbury, Cheshire	Western terminus of Route 68
	Middlebury	18.07	29.08	Route 188 west – Middlebury Center	Eastern terminus of Route 188
		18.97	30.53	I-84 west – Danbury	Exit 17 on I-84
		19.39	31.21	Route 64 to I-84 east – Middlebury, Waterbury
Litchfield	Watertown	22.93	36.90	Route 73 south – Oakville	Northern terminus of Route 73
		24.11	38.80	To US 6 west – Woodbury	Access via SR 838
		24.20	38.95	US 6 – Woodbury, Thomaston
		27.35	44.02	Route 132 south – Bethlehem	Northern terminus of Route 132
	Morris	30.81	49.58	Route 109 – Morris, Thomaston
		32.18	51.79	Route 61 south – Bethlehem, Morris	Northern terminus of Route 61
	Litchfield	34.91	56.18	Route 118 east – Harwinton	Western terminus of Route 118
		34.95	56.25	US 202 east – Torrington	Southern end of US 202 concurrency
		34.99	56.31	US 202 west – New Milford	Northern end of US 202 concurrency
	Goshen	41.18	66.27	Route 4 – Cornwall, Torrington	Roundabout
	Cornwall	47.62	76.64	Route 43 south – Cornwall	Northern terminus of Route 43
	Canaan	51.21	82.41	Route 126 north – Falls Village	Southern terminus of Route 126
		52.46	84.43	To US 7 south – Sharon	Access via SR 812
		52.57	84.60	US 7 – Sharon, Canaan, Norfolk, Sheffield	Northern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus       Incomplete access