We find that US cross-listing of Canadian stocks enhances domestic high-frequency trading (HFT) activity in the form of both opportunistic trading and market-making. First, US cross-listing boosts HFT low-latency cross-border arbitrage. This highly correlated HFT arbitrage activity across markets enhances stock price efficiency by correcting mispricing. Second, US cross-listing leads to an increase in news trading activity by high-frequency traders around US public macro-news releases. Finally, cross-listing increases a stock’s reliance on high-frequency market makers to provide liquidity. Yet, we find no evidence of higher fragility in liquidity supply after cross-listing.